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It was suggested that the underflow/overflow protection
should probably throw some sort of warning out, rather
than just silently fixing the issue.
So this patch adds some warnings here. The flag variables
used are not protected by locks, but since we can't print
from the reading functions, just being able to say we
saw an issue in the update interval is useful enough,
and can be slightly racy without real consequence.
The big complication is that we're only under a read
seqlock, so the data could shift under us during
our calculation to see if there was a problem. This
patch avoids this issue by nesting another seqlock
which allows us to snapshot the just required values
atomically. So we shouldn't see false positives.
I also added some basic rate-limiting here, since
on one build machine w/ skewed TSCs it was fairly
noisy at bootup.
Signed-off-by: John Stultz <john.stultz@linaro.org>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1426133800-29329-8-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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In the case where there is a broken clocksource
where there are multiple actual clocks that
aren't perfectly aligned, we may see small "negative"
deltas when we subtract 'now' from 'cycle_last'.
The values are actually negative with respect to the
clocksource mask value, not necessarily negative
if cast to a s64, but we can check by checking the
delta to see if it is a small (relative to the mask)
negative value (again negative relative to the mask).
If so, we assume we jumped backwards somehow and
instead use zero for our delta.
Signed-off-by: John Stultz <john.stultz@linaro.org>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1426133800-29329-7-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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When calculating the current delta since the last tick, we
currently have no hard protections to prevent a multiplication
overflow from occuring.
This patch introduces infrastructure to allow a cap that
limits the clocksource read delta value to the 'max_cycles' value,
which is where an overflow would occur.
Since this is in the hotpath, it adds the extra checking under
CONFIG_DEBUG_TIMEKEEPING=y.
There was some concern that capping time like this could cause
problems as we may stop expiring timers, which could go circular
if the timer that triggers time accumulation were mis-scheduled
too far in the future, which would cause time to stop.
However, since the mult overflow would result in a smaller time
value, we would effectively have the same problem there.
Signed-off-by: John Stultz <john.stultz@linaro.org>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1426133800-29329-6-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Recently there's been requests for better sanity
checking in the time code, so that it's more clear
when something is going wrong, since timekeeping issues
could manifest in a large number of strange ways in
various subsystems.
Thus, this patch adds some extra infrastructure to
add a check to update_wall_time() to print two new
warnings:
1) if we see the call delayed beyond the 'max_cycles'
overflow point,
2) or if we see the call delayed beyond the clocksource's
'max_idle_ns' value, which is currently 50% of the
overflow point.
This extra infrastructure is conditional on
a new CONFIG_DEBUG_TIMEKEEPING option, also
added in this patch - default off.
Tested this a bit by halting qemu for specified
lengths of time to trigger the warnings.
Signed-off-by: John Stultz <john.stultz@linaro.org>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1426133800-29329-5-git-send-email-john.stultz@linaro.org
[ Improved the changelog and the messages a bit. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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In order to facilitate clocksource validation, add a
'max_cycles' field to the clocksource structure which
will hold the maximum cycle value that can safely be
multiplied without potentially causing an overflow.
Signed-off-by: John Stultz <john.stultz@linaro.org>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1426133800-29329-4-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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The clocksource logic has a number of places where we try to
include a safety margin. Most of these are 12% safety margins,
but they are inconsistently applied and sometimes are applied
on top of each other.
Additionally, in the previous patch, we corrected an issue
where we unintentionally in effect created a 50% safety margin,
which these 12.5% margins where then added to.
So to simplify the logic here, this patch removes the various
12.5% margins, and consolidates adding the margin in one place:
clocks_calc_max_nsecs().
Additionally, Linus prefers a 50% safety margin, as it allows
bad clock values to be more easily caught. This should really
have no net effect, due to the corrected issue earlier which
caused greater then 50% margins to be used w/o issue.
Signed-off-by: John Stultz <john.stultz@linaro.org>
Acked-by: Stephen Boyd <sboyd@codeaurora.org> (for the sched_clock.c bit)
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1426133800-29329-3-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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The previous clocks_calc_max_nsecs() code had some unecessarily
complex bit logic to find the max interval that could cause
multiplication overflows. Since this is not in the hot
path, just do the divide to make it easier to read.
The previous implementation also had a subtle issue
that it avoided overflows with signed 64-bit values, where
as the intervals are always unsigned. This resulted in
overly conservative intervals, which other safety margins
were then added to, reducing the intended interval length.
Signed-off-by: John Stultz <john.stultz@linaro.org>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1426133800-29329-2-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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more changes
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It is not possible for the clockevents core to know which modes (other than
those with a corresponding feature flag) are supported by a particular
implementation. And drivers are expected to handle transition to all modes
elegantly, as ->set_mode() would be issued for them unconditionally.
Now, adding support for a new mode complicates things a bit if we want to use
the legacy ->set_mode() callback. We need to closely review all clockevents
drivers to see if they would break on addition of a new mode. And after such
reviews, it is found that we have to do non-trivial changes to most of the
drivers [1].
Introduce mode-specific set_mode_*() callbacks, some of which the drivers may or
may not implement. A missing callback would clearly convey the message that the
corresponding mode isn't supported.
A driver may still choose to keep supporting the legacy ->set_mode() callback,
but ->set_mode() wouldn't be supporting any new modes beyond RESUME. If a driver
wants to benefit from using a new mode, it would be required to migrate to
the mode specific callbacks.
The legacy ->set_mode() callback and the newly introduced mode-specific
callbacks are mutually exclusive. Only one of them should be supported by the
driver.
Sanity check is done at the time of registration to distinguish between optional
and required callbacks and to make error recovery and handling simpler. If the
legacy ->set_mode() callback is provided, all mode specific ones would be
ignored by the core but a warning is thrown if they are present.
Call sites calling ->set_mode() directly are also updated to use
__clockevents_set_mode() instead, as ->set_mode() may not be available anymore
for few drivers.
[1] https://lkml.org/lkml/2014/12/9/605
[2] https://lkml.org/lkml/2015/1/23/255
Suggested-by: Thomas Gleixner <tglx@linutronix.de> [2]
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Cc: linaro-kernel@lists.linaro.org
Cc: linaro-networking@linaro.org
Link: http://lkml.kernel.org/r/792d59a40423f0acffc9bb0bec9de1341a06fa02.1423788565.git.viresh.kumar@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull scheduler changes from Ingo Molnar:
"Major changes:
- Reworked CPU capacity code, for better SMP load balancing on
systems with assymetric CPUs. (Vincent Guittot, Morten Rasmussen)
- Reworked RT task SMP balancing to be push based instead of pull
based, to reduce latencies on large CPU count systems. (Steven
Rostedt)
- SCHED_DEADLINE support updates and fixes. (Juri Lelli)
- SCHED_DEADLINE task migration support during CPU hotplug. (Wanpeng Li)
- x86 mwait-idle optimizations and fixes. (Mike Galbraith, Len Brown)
- sched/numa improvements. (Rik van Riel)
- various cleanups"
* 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (28 commits)
sched/core: Drop debugging leftover trace_printk call
sched/deadline: Support DL task migration during CPU hotplug
sched/core: Check for available DL bandwidth in cpuset_cpu_inactive()
sched/deadline: Always enqueue on previous rq when dl_task_timer() fires
sched/core: Remove unused argument from init_[rt|dl]_rq()
sched/deadline: Fix rt runtime corruption when dl fails its global constraints
sched/deadline: Avoid a superfluous check
sched: Improve load balancing in the presence of idle CPUs
sched: Optimize freq invariant accounting
sched: Move CFS tasks to CPUs with higher capacity
sched: Add SD_PREFER_SIBLING for SMT level
sched: Remove unused struct sched_group_capacity::capacity_orig
sched: Replace capacity_factor by usage
sched: Calculate CPU's usage statistic and put it into struct sg_lb_stats::group_usage
sched: Add struct rq::cpu_capacity_orig
sched: Make scale_rt invariant with frequency
sched: Make sched entity usage tracking scale-invariant
sched: Remove frequency scaling from cpu_capacity
sched: Track group sched_entity usage contributions
sched: Add sched_avg::utilization_avg_contrib
...
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Commit:
3c18d447b3b3 ("sched/core: Check for available DL bandwidth in cpuset_cpu_inactive()")
forgot a trace_printk() debugging piece in and Steve's banner screamed
in dmesg. Remove it.
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Juri Lelli <juri.lelli@arm.com>
Cc: Juri Lelli <juri.lelli@gmail.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1428050570-21041-1-git-send-email-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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I observed that DL tasks can't be migrated to other CPUs during CPU
hotplug, in addition, task may/may not be running again if CPU is
added back.
The root cause which I found is that DL tasks will be throtted and
removed from the DL rq after comsuming all their budget, which
leads to the situation that stop task can't pick them up from the
DL rq and migrate them to other CPUs during hotplug.
The method to reproduce:
schedtool -E -t 50000:100000 -e ./test
Actually './test' is just a simple for loop. Then observe which CPU the
test task is on and offline it:
echo 0 > /sys/devices/system/cpu/cpuN/online
This patch adds the DL task migration during CPU hotplug by finding a
most suitable later deadline rq after DL timer fires if current rq is
offline.
If it fails to find a suitable later deadline rq then it falls back to
any eligible online CPU in so that the deadline task will come back
to us, and the push/pull mechanism should then move it around properly.
Suggested-and-Acked-by: Juri Lelli <juri.lelli@arm.com>
Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1427411315-4298-1-git-send-email-wanpeng.li@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Hotplug operations are destructive w.r.t. cpusets. In case such an
operation is performed on a CPU belonging to an exlusive cpuset, the
DL bandwidth information associated with the corresponding root
domain is gone even if the operation fails (in sched_cpu_inactive()).
For this reason we need to move the check we currently have in
sched_cpu_inactive() to cpuset_cpu_inactive() to prevent useless
cpusets reconfiguration in the CPU_DOWN_FAILED path.
Signed-off-by: Juri Lelli <juri.lelli@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@gmail.com>
Link: http://lkml.kernel.org/r/1427792017-7356-2-git-send-email-juri.lelli@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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dl_task_timer() may fire on a different rq from where a task was removed
after throttling. Since the call path is:
dl_task_timer() ->
enqueue_task_dl() ->
enqueue_dl_entity() ->
replenish_dl_entity()
and replenish_dl_entity() uses dl_se's rq, we can't use current's rq
in dl_task_timer(), but we need to lock the task's previous one.
Tested-by: Wanpeng Li <wanpeng.li@linux.intel.com>
Signed-off-by: Juri Lelli <juri.lelli@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Kirill Tkhai <ktkhai@parallels.com>
Cc: Juri Lelli <juri.lelli@gmail.com>
Fixes: 3960c8c0c789 ("sched: Make dl_task_time() use task_rq_lock()")
Link: http://lkml.kernel.org/r/1427792017-7356-1-git-send-email-juri.lelli@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Obviously, 'rq' is not used in these two functions, therefore,
there is no reason for it to be passed as an argument.
Signed-off-by: Abel Vesa <abelvesa@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1425383427-26244-1-git-send-email-abelvesa@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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One version of sched_rt_global_constaints() (the !rt-cgroup one)
changes state, therefore if we fail the later sched_dl_global_constraints()
call the state is left in an inconsistent state.
Fix this by changing the order of the calls.
Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
[ Improved the changelog. ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Juri Lelli <juri.lelli@arm.com>
Link: http://lkml.kernel.org/r/1426590931-4639-2-git-send-email-wanpeng.li@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Since commit 40767b0dc768 ("sched/deadline: Fix deadline parameter
modification handling") we clear the thottled state when switching
from a dl task, therefore we should never find it set in switching to
a dl task.
Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
[ Improved the changelog. ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Juri Lelli <juri.lelli@arm.com>
Link: http://lkml.kernel.org/r/1426590931-4639-1-git-send-email-wanpeng.li@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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When a CPU is kicked to do nohz idle balancing, it wakes up to do load
balancing on itself, followed by load balancing on behalf of idle CPUs.
But it may end up with load after the load balancing attempt on itself.
This aborts nohz idle balancing. As a result several idle CPUs are left
without tasks till such a time that an ILB CPU finds it unfavorable to
pull tasks upon itself. This delays spreading of load across idle CPUs
and worse, clutters only a few CPUs with tasks.
The effect of the above problem was observed on an SMT8 POWER server
with 2 levels of numa domains. Busy loops equal to number of cores were
spawned. Since load balancing on fork/exec is discouraged across numa
domains, all busy loops would start on one of the numa domains. However
it was expected that eventually one busy loop would run per core across
all domains due to nohz idle load balancing. But it was observed that it
took as long as 10 seconds to spread the load across numa domains.
Further investigation showed that this was a consequence of the
following:
1. An ILB CPU was chosen from the first numa domain to trigger nohz idle
load balancing [Given the experiment, upto 6 CPUs per core could be
potentially idle in this domain.]
2. However the ILB CPU would call load_balance() on itself before
initiating nohz idle load balancing.
3. Given cores are SMT8, the ILB CPU had enough opportunities to pull
tasks from its sibling cores to even out load.
4. Now that the ILB CPU was no longer idle, it would abort nohz idle
load balancing
As a result the opportunities to spread load across numa domains were
lost until such a time that the cores within the first numa domain had
equal number of tasks among themselves. This is a pretty bad scenario,
since the cores within the first numa domain would have as many as 4
tasks each, while cores in the neighbouring numa domains would all
remain idle.
Fix this, by checking if a CPU was woken up to do nohz idle load
balancing, before it does load balancing upon itself. This way we allow
idle CPUs across the system to do load balancing which results in
quicker spread of load, instead of performing load balancing within the
local sched domain hierarchy of the ILB CPU alone under circumstances
such as above.
Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Jason Low <jason.low2@hp.com>
Cc: benh@kernel.crashing.org
Cc: daniel.lezcano@linaro.org
Cc: efault@gmx.de
Cc: iamjoonsoo.kim@lge.com
Cc: morten.rasmussen@arm.com
Cc: pjt@google.com
Cc: riel@redhat.com
Cc: srikar@linux.vnet.ibm.com
Cc: svaidy@linux.vnet.ibm.com
Cc: tim.c.chen@linux.intel.com
Cc: vincent.guittot@linaro.org
Link: http://lkml.kernel.org/r/20150326130014.21532.17158.stgit@preeti.in.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Currently the freq invariant accounting (in
__update_entity_runnable_avg() and sched_rt_avg_update()) get the
scale factor from a weak function call, this means that even for archs
that default on their implementation the compiler cannot see into this
function and optimize the extra scaling math away.
This is sad, esp. since its a 64-bit multiplication which can be quite
costly on some platforms.
So replace the weak function with #ifdef and __always_inline goo. This
is not quite as nice from an arch support PoV but should at least
result in compile time errors if done wrong.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Morten.Rasmussen@arm.com
Cc: Paul Turner <pjt@google.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: dietmar.eggemann@arm.com
Cc: efault@gmx.de
Cc: kamalesh@linux.vnet.ibm.com
Cc: nicolas.pitre@linaro.org
Cc: preeti@linux.vnet.ibm.com
Cc: riel@redhat.com
Link: http://lkml.kernel.org/r/20150323131905.GF23123@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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When a CPU is used to handle a lot of IRQs or some RT tasks, the remaining
capacity for CFS tasks can be significantly reduced. Once we detect such
situation by comparing cpu_capacity_orig and cpu_capacity, we trig an idle
load balance to check if it's worth moving its tasks on an idle CPU.
It's worth trying to move the task before the CPU is fully utilized to
minimize the preemption by irq or RT tasks.
Once the idle load_balance has selected the busiest CPU, it will look for an
active load balance for only two cases:
- There is only 1 task on the busiest CPU.
- We haven't been able to move a task of the busiest rq.
A CPU with a reduced capacity is included in the 1st case, and it's worth to
actively migrate its task if the idle CPU has got more available capacity for
CFS tasks. This test has been added in need_active_balance.
As a sidenote, this will not generate more spurious ilb because we already
trig an ilb if there is more than 1 busy cpu. If this cpu is the only one that
has a task, we will trig the ilb once for migrating the task.
The nohz_kick_needed function has been cleaned up a bit while adding the new
test
env.src_cpu and env.src_rq must be set unconditionnally because they are used
in need_active_balance which is called even if busiest->nr_running equals 1
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Morten.Rasmussen@arm.com
Cc: dietmar.eggemann@arm.com
Cc: efault@gmx.de
Cc: kamalesh@linux.vnet.ibm.com
Cc: linaro-kernel@lists.linaro.org
Cc: nicolas.pitre@linaro.org
Cc: preeti@linux.vnet.ibm.com
Cc: riel@redhat.com
Link: http://lkml.kernel.org/r/1425052454-25797-12-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Add the SD_PREFER_SIBLING flag for SMT level in order to ensure that
the scheduler will place at least one task per core.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Preeti U. Murthy <preeti@linux.vnet.ibm.com>
Cc: Morten.Rasmussen@arm.com
Cc: dietmar.eggemann@arm.com
Cc: efault@gmx.de
Cc: kamalesh@linux.vnet.ibm.com
Cc: linaro-kernel@lists.linaro.org
Cc: nicolas.pitre@linaro.org
Cc: riel@redhat.com
Link: http://lkml.kernel.org/r/1425052454-25797-11-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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The 'struct sched_group_capacity::capacity_orig' field is no longer used
in the scheduler so we can remove it.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Morten.Rasmussen@arm.com
Cc: dietmar.eggemann@arm.com
Cc: efault@gmx.de
Cc: kamalesh@linux.vnet.ibm.com
Cc: linaro-kernel@lists.linaro.org
Cc: nicolas.pitre@linaro.org
Cc: preeti@linux.vnet.ibm.com
Cc: riel@redhat.com
Link: http://lkml.kernel.org/r/1425378903-5349-1-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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The scheduler tries to compute how many tasks a group of CPUs can handle by
assuming that a task's load is SCHED_LOAD_SCALE and a CPU's capacity is
SCHED_CAPACITY_SCALE.
'struct sg_lb_stats:group_capacity_factor' divides the capacity of the group
by SCHED_LOAD_SCALE to estimate how many task can run in the group. Then, it
compares this value with the sum of nr_running to decide if the group is
overloaded or not.
But the 'group_capacity_factor' concept is hardly working for SMT systems, it
sometimes works for big cores but fails to do the right thing for little cores.
Below are two examples to illustrate the problem that this patch solves:
1- If the original capacity of a CPU is less than SCHED_CAPACITY_SCALE
(640 as an example), a group of 3 CPUS will have a max capacity_factor of 2
(div_round_closest(3x640/1024) = 2) which means that it will be seen as
overloaded even if we have only one task per CPU.
2 - If the original capacity of a CPU is greater than SCHED_CAPACITY_SCALE
(1512 as an example), a group of 4 CPUs will have a capacity_factor of 4
(at max and thanks to the fix [0] for SMT system that prevent the apparition
of ghost CPUs) but if one CPU is fully used by rt tasks (and its capacity is
reduced to nearly nothing), the capacity factor of the group will still be 4
(div_round_closest(3*1512/1024) = 5 which is cap to 4 with [0]).
So, this patch tries to solve this issue by removing capacity_factor and
replacing it with the 2 following metrics:
- The available CPU's capacity for CFS tasks which is already used by
load_balance().
- The usage of the CPU by the CFS tasks. For the latter, utilization_avg_contrib
has been re-introduced to compute the usage of a CPU by CFS tasks.
'group_capacity_factor' and 'group_has_free_capacity' has been removed and replaced
by 'group_no_capacity'. We compare the number of task with the number of CPUs and
we evaluate the level of utilization of the CPUs to define if a group is
overloaded or if a group has capacity to handle more tasks.
For SD_PREFER_SIBLING, a group is tagged overloaded if it has more than 1 task
so it will be selected in priority (among the overloaded groups). Since [1],
SD_PREFER_SIBLING is no more concerned by the computation of 'load_above_capacity'
because local is not overloaded.
[1] 9a5d9ba6a363 ("sched/fair: Allow calculate_imbalance() to move idle cpus")
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Morten.Rasmussen@arm.com
Cc: dietmar.eggemann@arm.com
Cc: efault@gmx.de
Cc: kamalesh@linux.vnet.ibm.com
Cc: linaro-kernel@lists.linaro.org
Cc: nicolas.pitre@linaro.org
Cc: preeti@linux.vnet.ibm.com
Cc: riel@redhat.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1425052454-25797-9-git-send-email-vincent.guittot@linaro.org
[ Tidied up the changelog. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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sg_lb_stats::group_usage
Monitor the usage level of each group of each sched_domain level. The usage is
the portion of cpu_capacity_orig that is currently used on a CPU or group of
CPUs. We use the utilization_load_avg to evaluate the usage level of each
group.
The utilization_load_avg only takes into account the running time of the CFS
tasks on a CPU with a maximum value of SCHED_LOAD_SCALE when the CPU is fully
utilized. Nevertheless, we must cap utilization_load_avg which can be
temporally greater than SCHED_LOAD_SCALE after the migration of a task on this
CPU and until the metrics are stabilized.
The utilization_load_avg is in the range [0..SCHED_LOAD_SCALE] to reflect the
running load on the CPU whereas the available capacity for the CFS task is in
the range [0..cpu_capacity_orig]. In order to test if a CPU is fully utilized
by CFS tasks, we have to scale the utilization in the cpu_capacity_orig range
of the CPU to get the usage of the latter. The usage can then be compared with
the available capacity (ie cpu_capacity) to deduct the usage level of a CPU.
The frequency scaling invariance of the usage is not taken into account in this
patch, it will be solved in another patch which will deal with frequency
scaling invariance on the utilization_load_avg.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Morten.Rasmussen@arm.com
Cc: dietmar.eggemann@arm.com
Cc: efault@gmx.de
Cc: kamalesh@linux.vnet.ibm.com
Cc: linaro-kernel@lists.linaro.org
Cc: nicolas.pitre@linaro.org
Cc: preeti@linux.vnet.ibm.com
Cc: riel@redhat.com
Link: http://lkml.kernel.org/r/1425455327-13508-1-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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This new field 'cpu_capacity_orig' reflects the original capacity of a CPU
before being altered by rt tasks and/or IRQ
The cpu_capacity_orig will be used:
- to detect when the capacity of a CPU has been noticeably reduced so we can
trig load balance to look for a CPU with better capacity. As an example, we
can detect when a CPU handles a significant amount of irq
(with CONFIG_IRQ_TIME_ACCOUNTING) but this CPU is seen as an idle CPU by
scheduler whereas CPUs, which are really idle, are available.
- evaluate the available capacity for CFS tasks
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Acked-by: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Morten.Rasmussen@arm.com
Cc: dietmar.eggemann@arm.com
Cc: efault@gmx.de
Cc: linaro-kernel@lists.linaro.org
Cc: nicolas.pitre@linaro.org
Cc: preeti@linux.vnet.ibm.com
Cc: riel@redhat.com
Link: http://lkml.kernel.org/r/1425052454-25797-7-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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The average running time of RT tasks is used to estimate the remaining compute
capacity for CFS tasks. This remaining capacity is the original capacity scaled
down by a factor (aka scale_rt_capacity). This estimation of available capacity
must also be invariant with frequency scaling.
A frequency scaling factor is applied on the running time of the RT tasks for
computing scale_rt_capacity.
In sched_rt_avg_update(), we now scale the RT execution time like below:
rq->rt_avg += rt_delta * arch_scale_freq_capacity() >> SCHED_CAPACITY_SHIFT
Then, scale_rt_capacity can be summarized by:
scale_rt_capacity = SCHED_CAPACITY_SCALE * available / total
with available = total - rq->rt_avg
This has been been optimized in current code by:
scale_rt_capacity = available / (total >> SCHED_CAPACITY_SHIFT)
But we can also developed the equation like below:
scale_rt_capacity = SCHED_CAPACITY_SCALE - ((rq->rt_avg << SCHED_CAPACITY_SHIFT) / total)
and we can optimize the equation by removing SCHED_CAPACITY_SHIFT shift in
the computation of rq->rt_avg and scale_rt_capacity().
so rq->rt_avg += rt_delta * arch_scale_freq_capacity()
and
scale_rt_capacity = SCHED_CAPACITY_SCALE - (rq->rt_avg / total)
arch_scale_frequency_capacity() will be called in the hot path of the scheduler
which implies to have a short and efficient function.
As an example, arch_scale_frequency_capacity() should return a cached value that
is updated periodically outside of the hot path.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Morten.Rasmussen@arm.com
Cc: dietmar.eggemann@arm.com
Cc: efault@gmx.de
Cc: kamalesh@linux.vnet.ibm.com
Cc: linaro-kernel@lists.linaro.org
Cc: nicolas.pitre@linaro.org
Cc: preeti@linux.vnet.ibm.com
Cc: riel@redhat.com
Link: http://lkml.kernel.org/r/1425052454-25797-6-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Apply frequency scale-invariance correction factor to usage tracking.
Each segment of the running_avg_sum geometric series is now scaled by the
current frequency so the utilization_avg_contrib of each entity will be
invariant with frequency scaling.
As a result, utilization_load_avg which is the sum of utilization_avg_contrib,
becomes invariant too. So the usage level that is returned by get_cpu_usage(),
stays relative to the max frequency as the cpu_capacity which is is compared against.
Then, we want the keep the load tracking values in a 32-bit type, which implies
that the max value of {runnable|running}_avg_sum must be lower than
2^32/88761=48388 (88761 is the max weigth of a task). As LOAD_AVG_MAX = 47742,
arch_scale_freq_capacity() must return a value less than
(48388/47742) << SCHED_CAPACITY_SHIFT = 1037 (SCHED_SCALE_CAPACITY = 1024).
So we define the range to [0..SCHED_SCALE_CAPACITY] in order to avoid overflow.
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Paul Turner <pjt@google.com>
Cc: Ben Segall <bsegall@google.com>
Cc: Ben Segall <bsegall@google.com>
Cc: Morten.Rasmussen@arm.com
Cc: Paul Turner <pjt@google.com>
Cc: dietmar.eggemann@arm.com
Cc: efault@gmx.de
Cc: kamalesh@linux.vnet.ibm.com
Cc: linaro-kernel@lists.linaro.org
Cc: nicolas.pitre@linaro.org
Cc: preeti@linux.vnet.ibm.com
Cc: riel@redhat.com
Link: http://lkml.kernel.org/r/1425455186-13451-1-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Now that arch_scale_cpu_capacity has been introduced to scale the original
capacity, the arch_scale_freq_capacity is no longer used (it was
previously used by ARM arch).
Remove arch_scale_freq_capacity from the computation of cpu_capacity.
The frequency invariance will be handled in the load tracking and not in
the CPU capacity. arch_scale_freq_capacity will be revisited for scaling
load with the current frequency of the CPUs in a later patch.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Morten.Rasmussen@arm.com
Cc: dietmar.eggemann@arm.com
Cc: efault@gmx.de
Cc: kamalesh@linux.vnet.ibm.com
Cc: linaro-kernel@lists.linaro.org
Cc: nicolas.pitre@linaro.org
Cc: preeti@linux.vnet.ibm.com
Cc: riel@redhat.com
Link: http://lkml.kernel.org/r/1425052454-25797-4-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Add usage contribution tracking for group entities. Unlike
se->avg.load_avg_contrib, se->avg.utilization_avg_contrib for group
entities is the sum of se->avg.utilization_avg_contrib for all entities on the
group runqueue.
It is _not_ influenced in any way by the task group h_load. Hence it is
representing the actual cpu usage of the group, not its intended load
contribution which may differ significantly from the utilization on
lightly utilized systems.
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Paul Turner <pjt@google.com>
Cc: Ben Segall <bsegall@google.com>
Cc: Ben Segall <bsegall@google.com>
Cc: Morten.Rasmussen@arm.com
Cc: Paul Turner <pjt@google.com>
Cc: dietmar.eggemann@arm.com
Cc: efault@gmx.de
Cc: kamalesh@linux.vnet.ibm.com
Cc: linaro-kernel@lists.linaro.org
Cc: nicolas.pitre@linaro.org
Cc: preeti@linux.vnet.ibm.com
Cc: riel@redhat.com
Link: http://lkml.kernel.org/r/1425052454-25797-3-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Add new statistics which reflect the average time a task is running on the CPU
and the sum of these running time of the tasks on a runqueue. The latter is
named utilization_load_avg.
This patch is based on the usage metric that was proposed in the 1st
versions of the per-entity load tracking patchset by Paul Turner
<pjt@google.com> but that has be removed afterwards. This version differs from
the original one in the sense that it's not linked to task_group.
The rq's utilization_load_avg will be used to check if a rq is overloaded or
not instead of trying to compute how many tasks a group of CPUs can handle.
Rename runnable_avg_period into avg_period as it is now used with both
runnable_avg_sum and running_avg_sum.
Add some descriptions of the variables to explain their differences.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Paul Turner <pjt@google.com>
Cc: Ben Segall <bsegall@google.com>
Cc: Ben Segall <bsegall@google.com>
Cc: Morten.Rasmussen@arm.com
Cc: Paul Turner <pjt@google.com>
Cc: dietmar.eggemann@arm.com
Cc: efault@gmx.de
Cc: kamalesh@linux.vnet.ibm.com
Cc: linaro-kernel@lists.linaro.org
Cc: nicolas.pitre@linaro.org
Cc: preeti@linux.vnet.ibm.com
Cc: riel@redhat.com
Link: http://lkml.kernel.org/r/1425052454-25797-2-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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applying new patches
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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This patch adds rq->clock update skip for SCHED_DEADLINE task yield,
to tell update_rq_clock() that we've just updated the clock, so that
we don't do a microscopic update in schedule() and double the
fastpath cost.
Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
Cc: Juri Lelli <juri.lelli@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1425961200-3809-1-git-send-email-wanpeng.li@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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If the CPU is running a realtime task that does not round-robin
with another realtime task of equal priority, there is no point
in keeping the scheduler tick going. After all, whenever the
scheduler tick runs, the kernel will just decide not to
reschedule.
Extend sched_can_stop_tick() to recognize these situations, and
inform the rest of the kernel that the scheduler tick can be
stopped.
Tested-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: fweisbec@redhat.com
Cc: mtosatti@redhat.com
Link: http://lkml.kernel.org/r/20150216152349.6a8ed824@annuminas.surriel.com
[ Small cleanliness tweak. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Commit 81907478c431 ("sched/fair: Avoid using uninitialized variable
in preferred_group_nid()") unconditionally initializes max_group with
NODE_MASK_NONE, this means that when !max_faults (max_group didn't get
set), we'll now continue the iteration with an empty mask.
Which in turn makes the actual body of the loop go away, so we'll just
iterate until completion; short circuit this by breaking out of the
loop as soon as this would happen.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20150209113727.GS5029@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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There is a subtle interaction between the logic introduced in commit
e63da03639cc ("sched/numa: Allow task switch if load imbalance improves"),
the way the load balancer counts the load on each NUMA node, and the way
NUMA hinting faults are done.
Specifically, the load balancer only counts currently running tasks
in the load, while NUMA hinting faults may cause tasks to stop, if
the page is locked by another task.
This could cause all of the threads of a large single instance workload,
like SPECjbb2005, to migrate to the same NUMA node. This was possible
because occasionally they all fault on the same few pages, and only one
of the threads remains runnable. That thread can move to the process's
preferred NUMA node without making the imbalance worse, because nothing
else is running at that time.
The fix is to check the direction of the net moving of load, and to
refuse a NUMA move if it would cause the system to move past the point
of balance. In an unbalanced state, only moves that bring us closer
to the balance point are allowed.
Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: mgorman@suse.de
Link: http://lkml.kernel.org/r/20150203165648.0e9ac692@annuminas.surriel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull core locking changes from Ingo Molnar:
"Main changes:
- jump label asm preparatory work for PowerPC (Anton Blanchard)
- rwsem optimizations and cleanups (Davidlohr Bueso)
- mutex optimizations and cleanups (Jason Low)
- futex fix (Oleg Nesterov)
- remove broken atomicity checks from {READ,WRITE}_ONCE() (Peter
Zijlstra)"
* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
powerpc, jump_label: Include linux/jump_label.h to get HAVE_JUMP_LABEL define
jump_label: Allow jump labels to be used in assembly
jump_label: Allow asm/jump_label.h to be included in assembly
locking/mutex: Further simplify mutex_spin_on_owner()
locking: Remove atomicy checks from {READ,WRITE}_ONCE
locking/rtmutex: Rename argument in the rt_mutex_adjust_prio_chain() documentation as well
locking/rwsem: Fix lock optimistic spinning when owner is not running
locking: Remove ACCESS_ONCE() usage
locking/rwsem: Check for active lock before bailing on spinning
locking/rwsem: Avoid deceiving lock spinners
locking/rwsem: Set lock ownership ASAP
locking/rwsem: Document barrier need when waking tasks
locking/futex: Check PF_KTHREAD rather than !p->mm to filter out kthreads
locking/mutex: Refactor mutex_spin_on_owner()
locking/mutex: In mutex_spin_on_owner(), return true when owner changes
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Similar to what Linus suggested for rwsem_spin_on_owner(), in
mutex_spin_on_owner() instead of having while (true) and
breaking out of the spin loop on lock->owner != owner, we can
have the loop directly check for while (lock->owner == owner) to
improve the readability of the code.
It also shrinks the code a bit:
text data bss dec hex filename
3721 0 0 3721 e89 mutex.o.before
3705 0 0 3705 e79 mutex.o.after
Signed-off-by: Jason Low <jason.low2@hp.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Link: http://lkml.kernel.org/r/1428521960-5268-2-git-send-email-jason.low2@hp.com
[ Added code generation info. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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documentation as well
The following commit changed "deadlock_detect" to "chwalk":
8930ed80f970 ("rtmutex: Cleanup deadlock detector debug logic")
do that rename in the function's documentation as well.
Signed-off-by: Tom(JeHyeon) Yeon <tom.yeon@windriver.com>
Cc: peterz@infradead.org
Link: http://lkml.kernel.org/r/1426655010-31651-1-git-send-email-tom.yeon@windriver.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Ming reported soft lockups occurring when running xfstest due to
the following tip:locking/core commit:
b3fd4f03ca0b ("locking/rwsem: Avoid deceiving lock spinners")
When doing optimistic spinning in rwsem, threads should stop
spinning when the lock owner is not running. While a thread is
spinning on owner, if the owner reschedules, owner->on_cpu
returns false and we stop spinning.
However, this commit essentially caused the check to get
ignored because when we break out of the spin loop due to
!on_cpu, we continue spinning if sem->owner != NULL.
This patch fixes this by making sure we stop spinning if the
owner is not running. Furthermore, just like with mutexes,
refactor the code such that we don't have separate checks for
owner_running(). This makes it more straightforward in terms of
why we exit the spin on owner loop and we would also avoid
needing to "guess" why we broke out of the loop to make this
more readable.
Reported-and-tested-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Jason Low <jason.low2@hp.com>
Acked-by: Davidlohr Bueso <dave@stgolabs.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michel Lespinasse <walken@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Link: http://lkml.kernel.org/r/1425714331.2475.388.camel@j-VirtualBox
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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With the new standardized functions, we can replace all
ACCESS_ONCE() calls across relevant locking - this includes
lockref and seqlock while at it.
ACCESS_ONCE() does not work reliably on non-scalar types.
For example gcc 4.6 and 4.7 might remove the volatile tag
for such accesses during the SRA (scalar replacement of
aggregates) step:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145
Update the new calls regardless of if it is a scalar type,
this is cleaner than having three alternatives.
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/1424662301.6539.18.camel@stgolabs.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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new changes
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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37e9562453b ("locking/rwsem: Allow conservative optimistic
spinning when readers have lock") forced the default for
optimistic spinning to be disabled if the lock owner was
nil, which makes much sense for readers. However, while
it is not our priority, we can make some optimizations
for write-mostly workloads. We can bail the spinning step
and still be conservative if there are any active tasks,
otherwise there's really no reason not to spin, as the
semaphore is most likely unlocked.
This patch recovers most of a Unixbench 'execl' benchmark
throughput by sleeping less and making better average system
usage:
before:
CPU %user %nice %system %iowait %steal %idle
all 0.60 0.00 8.02 0.00 0.00 91.38
after:
CPU %user %nice %system %iowait %steal %idle
all 1.22 0.00 70.18 0.00 0.00 28.60
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Jason Low <jason.low2@hp.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michel Lespinasse <walken@google.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Link: http://lkml.kernel.org/r/1422609267-15102-6-git-send-email-dave@stgolabs.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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When readers hold the semaphore, the ->owner is nil. As such,
and unlike mutexes, '!owner' does not necessarily imply that
the lock is free. This will cause writers to potentially spin
excessively as they've been mislead to thinking they have a
chance of acquiring the lock, instead of blocking.
This patch therefore enhances the counter check when the owner
is not set by the time we've broken out of the loop. Otherwise
we can return true as a new owner has the lock and thus we want
to continue spinning. While at it, we can make rwsem_spin_on_owner()
less ambiguos and return right away under need_resched conditions.
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Jason Low <jason.low2@hp.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michel Lespinasse <walken@google.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Link: http://lkml.kernel.org/r/1422609267-15102-5-git-send-email-dave@stgolabs.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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In order to optimize the spinning step, we need to set the lock
owner as soon as the lock is acquired; after a successful counter
cmpxchg operation, that is. This is particularly useful as rwsems
need to set the owner to nil for readers, so there is a greater
chance of falling out of the spinning. Currently we only set the
owner much later in the game, in the more generic level -- latency
can be specially bad when waiting for a node->next pointer when
releasing the osq in up_write calls.
As such, update the owner inside rwsem_try_write_lock (when the
lock is obtained after blocking) and rwsem_try_write_lock_unqueued
(when the lock is obtained while spinning). This requires creating
a new internal rwsem.h header to share the owner related calls.
Also cleanup some headers for mutex and rwsem.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Jason Low <jason.low2@hp.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michel Lespinasse <walken@google.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Link: http://lkml.kernel.org/r/1422609267-15102-4-git-send-email-dave@stgolabs.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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The need for the smp_mb() in __rwsem_do_wake() should be
properly documented. Applies to both xadd and spinlock
variants.
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Jason Low <jason.low2@hp.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michel Lespinasse <walken@google.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Link: http://lkml.kernel.org/r/1422609267-15102-3-git-send-email-dave@stgolabs.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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attach_to_pi_owner() checks p->mm to prevent attaching to kthreads and
this looks doubly wrong:
1. It should actually check PF_KTHREAD, kthread can do use_mm().
2. If this task is not kthread and it is actually the lock owner we can
wrongly return -EPERM instead of -ESRCH or retry-if-EAGAIN.
And note that this wrong EPERM is the likely case unless the exiting
task is (auto)reaped quickly, we check ->mm before PF_EXITING.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Darren Hart <darren@dvhart.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Larry Woodman <lwoodman@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mateusz Guzik <mguzik@redhat.com>
Link: http://lkml.kernel.org/r/20150202140536.GA26406@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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As suggested by Davidlohr, we could refactor mutex_spin_on_owner().
Currently, we split up owner_running() with mutex_spin_on_owner().
When the owner changes, we make duplicate owner checks which are not
necessary. It also makes the code a bit obscure as we are using a
second check to figure out why we broke out of the loop.
This patch modifies it such that we remove the owner_running() function
and the mutex_spin_on_owner() loop directly checks for if the owner changes,
if the owner is not running, or if we need to reschedule. If the owner
changes, we break out of the loop and return true. If the owner is not
running or if we need to reschedule, then break out of the loop and return
false.
Suggested-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Jason Low <jason.low2@hp.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: chegu_vinod@hp.com
Cc: tglx@linutronix.de
Link: http://lkml.kernel.org/r/1422914367-5574-3-git-send-email-jason.low2@hp.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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In the mutex_spin_on_owner(), we return true only if lock->owner == NULL.
This was beneficial in situations where there were multiple threads
simultaneously spinning for the mutex. If another thread got the lock
while other spinner(s) were also doing mutex_spin_on_owner(), then the
other spinners would stop spinning. This workaround helped reduce the
chance that many spinners were simultaneously spinning for the mutex
which can help reduce contention in highly contended cases.
However, recent changes were made to the optimistic spinning code such
that instead of having all spinners simultaneously spin for the mutex,
we queue the spinners with an MCS lock such that only one thread spins
for the mutex at a time. Furthermore, the OSQ optimizations ensure that
spinners in the queue will stop waiting if it needs to reschedule.
Now, we don't have to worry about multiple threads spinning on owner
at the same time, and if lock->owner is not NULL at this point, it likely
means another thread happens to obtain the lock in the fastpath. In this
case, it would make sense for the spinner to continue spinning as long
as the spinner doesn't need to schedule and the mutex owner is running.
This patch changes this so that mutex_spin_on_owner() returns true when
the lock owner changes, which means a thread will only stop spinning
if it either needs to reschedule or if the lock owner is not running.
We saw up to a 5% performance improvement in the fserver workload with
this patch.
Signed-off-by: Jason Low <jason.low2@hp.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Davidlohr Bueso <dave@stgolabs.net>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: chegu_vinod@hp.com
Cc: tglx@linutronix.de
Link: http://lkml.kernel.org/r/1422914367-5574-2-git-send-email-jason.low2@hp.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Pull KVM updates from Paolo Bonzini:
"First batch of KVM changes for 4.1
The most interesting bit here is irqfd/ioeventfd support for ARM and
ARM64.
Summary:
ARM/ARM64:
fixes for live migration, irqfd and ioeventfd support (enabling
vhost, too), page aging
s390:
interrupt handling rework, allowing to inject all local interrupts
via new ioctl and to get/set the full local irq state for migration
and introspection. New ioctls to access memory by virtual address,
and to get/set the guest storage keys. SIMD support.
MIPS:
FPU and MIPS SIMD Architecture (MSA) support. Includes some
patches from Ralf Baechle's MIPS tree.
x86:
bugfixes (notably for pvclock, the others are small) and cleanups.
Another small latency improvement for the TSC deadline timer"
* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: (146 commits)
KVM: use slowpath for cross page cached accesses
kvm: mmu: lazy collapse small sptes into large sptes
KVM: x86: Clear CR2 on VCPU reset
KVM: x86: DR0-DR3 are not clear on reset
KVM: x86: BSP in MSR_IA32_APICBASE is writable
KVM: x86: simplify kvm_apic_map
KVM: x86: avoid logical_map when it is invalid
KVM: x86: fix mixed APIC mode broadcast
KVM: x86: use MDA for interrupt matching
kvm/ppc/mpic: drop unused IRQ_testbit
KVM: nVMX: remove unnecessary double caching of MAXPHYADDR
KVM: nVMX: checks for address bits beyond MAXPHYADDR on VM-entry
KVM: x86: cache maxphyaddr CPUID leaf in struct kvm_vcpu
KVM: vmx: pass error code with internal error #2
x86: vdso: fix pvclock races with task migration
KVM: remove kvm_read_hva and kvm_read_hva_atomic
KVM: x86: optimize delivery of TSC deadline timer interrupt
KVM: x86: extract blocking logic from __vcpu_run
kvm: x86: fix x86 eflags fixed bit
KVM: s390: migrate vcpu interrupt state
...
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