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authorIngo Molnar <mingo@kernel.org>2013-08-14 17:58:56 +0200
committerIngo Molnar <mingo@kernel.org>2013-08-14 17:58:56 +0200
commit6f1d657668ac3041b65265d3653d7e9172a0d603 (patch)
tree6e837c683783708637cc4caf9de759166c7469b7 /kernel
parentd4e4ab86bcba5a72779c43dc1459f71fea3d89c8 (diff)
parentd13508f9440e46dccac6a2dd48d51a73b2207482 (diff)
downloadop-kernel-dev-6f1d657668ac3041b65265d3653d7e9172a0d603.zip
op-kernel-dev-6f1d657668ac3041b65265d3653d7e9172a0d603.tar.gz
Merge branch 'timers/nohz-v3' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks into timers/nohz
Pull nohz improvements from Frederic Weisbecker: " It mostly contains fixes and full dynticks off-case optimizations. I believe that distros want to enable this feature so it seems important to optimize the case where the "nohz_full=" parameter is empty. ie: I'm trying to remove any performance regression that comes with NO_HZ_FULL=y when the feature is not used. This patchset improves the current situation a lot (off-case appears to be around 11% faster with hackbench, although I guess it may vary depending on the configuration but it should be significantly faster in any case) now there is still some work to do: I can still observe a remaining loss of 1.6% throughput seen with hackbench compared to CONFIG_NO_HZ_FULL=n. " Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/context_tracking.c125
-rw-r--r--kernel/sched/core.c4
-rw-r--r--kernel/sched/cputime.c53
-rw-r--r--kernel/time/Kconfig1
-rw-r--r--kernel/time/sched_clock.c2
-rw-r--r--kernel/time/tick-sched.c59
6 files changed, 116 insertions, 128 deletions
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 383f823..247091b 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -20,22 +20,33 @@
#include <linux/hardirq.h>
#include <linux/export.h>
-DEFINE_PER_CPU(struct context_tracking, context_tracking) = {
-#ifdef CONFIG_CONTEXT_TRACKING_FORCE
- .active = true,
-#endif
-};
+#define CREATE_TRACE_POINTS
+#include <trace/events/context_tracking.h>
+
+struct static_key context_tracking_enabled = STATIC_KEY_INIT_FALSE;
+EXPORT_SYMBOL_GPL(context_tracking_enabled);
+
+DEFINE_PER_CPU(struct context_tracking, context_tracking);
+EXPORT_SYMBOL_GPL(context_tracking);
+
+void context_tracking_cpu_set(int cpu)
+{
+ if (!per_cpu(context_tracking.active, cpu)) {
+ per_cpu(context_tracking.active, cpu) = true;
+ static_key_slow_inc(&context_tracking_enabled);
+ }
+}
/**
- * user_enter - Inform the context tracking that the CPU is going to
- * enter userspace mode.
+ * context_tracking_user_enter - Inform the context tracking that the CPU is going to
+ * enter userspace mode.
*
* This function must be called right before we switch from the kernel
* to userspace, when it's guaranteed the remaining kernel instructions
* to execute won't use any RCU read side critical section because this
* function sets RCU in extended quiescent state.
*/
-void user_enter(void)
+void context_tracking_user_enter(void)
{
unsigned long flags;
@@ -54,17 +65,32 @@ void user_enter(void)
WARN_ON_ONCE(!current->mm);
local_irq_save(flags);
- if (__this_cpu_read(context_tracking.active) &&
- __this_cpu_read(context_tracking.state) != IN_USER) {
+ if ( __this_cpu_read(context_tracking.state) != IN_USER) {
+ if (__this_cpu_read(context_tracking.active)) {
+ trace_user_enter(0);
+ /*
+ * At this stage, only low level arch entry code remains and
+ * then we'll run in userspace. We can assume there won't be
+ * any RCU read-side critical section until the next call to
+ * user_exit() or rcu_irq_enter(). Let's remove RCU's dependency
+ * on the tick.
+ */
+ vtime_user_enter(current);
+ rcu_user_enter();
+ }
/*
- * At this stage, only low level arch entry code remains and
- * then we'll run in userspace. We can assume there won't be
- * any RCU read-side critical section until the next call to
- * user_exit() or rcu_irq_enter(). Let's remove RCU's dependency
- * on the tick.
+ * Even if context tracking is disabled on this CPU, because it's outside
+ * the full dynticks mask for example, we still have to keep track of the
+ * context transitions and states to prevent inconsistency on those of
+ * other CPUs.
+ * If a task triggers an exception in userspace, sleep on the exception
+ * handler and then migrate to another CPU, that new CPU must know where
+ * the exception returns by the time we call exception_exit().
+ * This information can only be provided by the previous CPU when it called
+ * exception_enter().
+ * OTOH we can spare the calls to vtime and RCU when context_tracking.active
+ * is false because we know that CPU is not tickless.
*/
- vtime_user_enter(current);
- rcu_user_enter();
__this_cpu_write(context_tracking.state, IN_USER);
}
local_irq_restore(flags);
@@ -87,10 +113,9 @@ void user_enter(void)
*/
void __sched notrace preempt_schedule_context(void)
{
- struct thread_info *ti = current_thread_info();
enum ctx_state prev_ctx;
- if (likely(ti->preempt_count || irqs_disabled()))
+ if (likely(!preemptible()))
return;
/*
@@ -112,8 +137,8 @@ EXPORT_SYMBOL_GPL(preempt_schedule_context);
#endif /* CONFIG_PREEMPT */
/**
- * user_exit - Inform the context tracking that the CPU is
- * exiting userspace mode and entering the kernel.
+ * context_tracking_user_exit - Inform the context tracking that the CPU is
+ * exiting userspace mode and entering the kernel.
*
* This function must be called after we entered the kernel from userspace
* before any use of RCU read side critical section. This potentially include
@@ -122,7 +147,7 @@ EXPORT_SYMBOL_GPL(preempt_schedule_context);
* This call supports re-entrancy. This way it can be called from any exception
* handler without needing to know if we came from userspace or not.
*/
-void user_exit(void)
+void context_tracking_user_exit(void)
{
unsigned long flags;
@@ -131,38 +156,22 @@ void user_exit(void)
local_irq_save(flags);
if (__this_cpu_read(context_tracking.state) == IN_USER) {
- /*
- * We are going to run code that may use RCU. Inform
- * RCU core about that (ie: we may need the tick again).
- */
- rcu_user_exit();
- vtime_user_exit(current);
+ if (__this_cpu_read(context_tracking.active)) {
+ /*
+ * We are going to run code that may use RCU. Inform
+ * RCU core about that (ie: we may need the tick again).
+ */
+ rcu_user_exit();
+ vtime_user_exit(current);
+ trace_user_exit(0);
+ }
__this_cpu_write(context_tracking.state, IN_KERNEL);
}
local_irq_restore(flags);
}
-void guest_enter(void)
-{
- if (vtime_accounting_enabled())
- vtime_guest_enter(current);
- else
- __guest_enter();
-}
-EXPORT_SYMBOL_GPL(guest_enter);
-
-void guest_exit(void)
-{
- if (vtime_accounting_enabled())
- vtime_guest_exit(current);
- else
- __guest_exit();
-}
-EXPORT_SYMBOL_GPL(guest_exit);
-
-
/**
- * context_tracking_task_switch - context switch the syscall callbacks
+ * __context_tracking_task_switch - context switch the syscall callbacks
* @prev: the task that is being switched out
* @next: the task that is being switched in
*
@@ -174,11 +183,19 @@ EXPORT_SYMBOL_GPL(guest_exit);
* migrate to some CPU that doesn't do the context tracking. As such the TIF
* flag may not be desired there.
*/
-void context_tracking_task_switch(struct task_struct *prev,
- struct task_struct *next)
+void __context_tracking_task_switch(struct task_struct *prev,
+ struct task_struct *next)
{
- if (__this_cpu_read(context_tracking.active)) {
- clear_tsk_thread_flag(prev, TIF_NOHZ);
- set_tsk_thread_flag(next, TIF_NOHZ);
- }
+ clear_tsk_thread_flag(prev, TIF_NOHZ);
+ set_tsk_thread_flag(next, TIF_NOHZ);
}
+
+#ifdef CONFIG_CONTEXT_TRACKING_FORCE
+void __init context_tracking_init(void)
+{
+ int cpu;
+
+ for_each_possible_cpu(cpu)
+ context_tracking_cpu_set(cpu);
+}
+#endif
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b7c32cb..3fb7ace 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2510,13 +2510,11 @@ void __sched schedule_preempt_disabled(void)
*/
asmlinkage void __sched notrace preempt_schedule(void)
{
- struct thread_info *ti = current_thread_info();
-
/*
* If there is a non-zero preempt_count or interrupts are disabled,
* we do not want to preempt the current task. Just return..
*/
- if (likely(ti->preempt_count || irqs_disabled()))
+ if (likely(!preemptible()))
return;
do {
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index a7959e0..c1d7493 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -378,11 +378,8 @@ static inline void irqtime_account_process_tick(struct task_struct *p, int user_
#ifdef CONFIG_VIRT_CPU_ACCOUNTING
#ifndef __ARCH_HAS_VTIME_TASK_SWITCH
-void vtime_task_switch(struct task_struct *prev)
+void vtime_common_task_switch(struct task_struct *prev)
{
- if (!vtime_accounting_enabled())
- return;
-
if (is_idle_task(prev))
vtime_account_idle(prev);
else
@@ -404,11 +401,8 @@ void vtime_task_switch(struct task_struct *prev)
* vtime_account().
*/
#ifndef __ARCH_HAS_VTIME_ACCOUNT
-void vtime_account_irq_enter(struct task_struct *tsk)
+void vtime_common_account_irq_enter(struct task_struct *tsk)
{
- if (!vtime_accounting_enabled())
- return;
-
if (!in_interrupt()) {
/*
* If we interrupted user, context_tracking_in_user()
@@ -428,7 +422,7 @@ void vtime_account_irq_enter(struct task_struct *tsk)
}
vtime_account_system(tsk);
}
-EXPORT_SYMBOL_GPL(vtime_account_irq_enter);
+EXPORT_SYMBOL_GPL(vtime_common_account_irq_enter);
#endif /* __ARCH_HAS_VTIME_ACCOUNT */
#endif /* CONFIG_VIRT_CPU_ACCOUNTING */
@@ -559,12 +553,6 @@ static void cputime_adjust(struct task_cputime *curr,
{
cputime_t rtime, stime, utime, total;
- if (vtime_accounting_enabled()) {
- *ut = curr->utime;
- *st = curr->stime;
- return;
- }
-
stime = curr->stime;
total = stime + curr->utime;
@@ -664,23 +652,17 @@ static void __vtime_account_system(struct task_struct *tsk)
void vtime_account_system(struct task_struct *tsk)
{
- if (!vtime_accounting_enabled())
- return;
-
write_seqlock(&tsk->vtime_seqlock);
__vtime_account_system(tsk);
write_sequnlock(&tsk->vtime_seqlock);
}
-void vtime_account_irq_exit(struct task_struct *tsk)
+void vtime_gen_account_irq_exit(struct task_struct *tsk)
{
- if (!vtime_accounting_enabled())
- return;
-
write_seqlock(&tsk->vtime_seqlock);
+ __vtime_account_system(tsk);
if (context_tracking_in_user())
tsk->vtime_snap_whence = VTIME_USER;
- __vtime_account_system(tsk);
write_sequnlock(&tsk->vtime_seqlock);
}
@@ -688,12 +670,8 @@ void vtime_account_user(struct task_struct *tsk)
{
cputime_t delta_cpu;
- if (!vtime_accounting_enabled())
- return;
-
- delta_cpu = get_vtime_delta(tsk);
-
write_seqlock(&tsk->vtime_seqlock);
+ delta_cpu = get_vtime_delta(tsk);
tsk->vtime_snap_whence = VTIME_SYS;
account_user_time(tsk, delta_cpu, cputime_to_scaled(delta_cpu));
write_sequnlock(&tsk->vtime_seqlock);
@@ -701,22 +679,27 @@ void vtime_account_user(struct task_struct *tsk)
void vtime_user_enter(struct task_struct *tsk)
{
- if (!vtime_accounting_enabled())
- return;
-
write_seqlock(&tsk->vtime_seqlock);
- tsk->vtime_snap_whence = VTIME_USER;
__vtime_account_system(tsk);
+ tsk->vtime_snap_whence = VTIME_USER;
write_sequnlock(&tsk->vtime_seqlock);
}
void vtime_guest_enter(struct task_struct *tsk)
{
+ /*
+ * The flags must be updated under the lock with
+ * the vtime_snap flush and update.
+ * That enforces a right ordering and update sequence
+ * synchronization against the reader (task_gtime())
+ * that can thus safely catch up with a tickless delta.
+ */
write_seqlock(&tsk->vtime_seqlock);
__vtime_account_system(tsk);
current->flags |= PF_VCPU;
write_sequnlock(&tsk->vtime_seqlock);
}
+EXPORT_SYMBOL_GPL(vtime_guest_enter);
void vtime_guest_exit(struct task_struct *tsk)
{
@@ -725,6 +708,7 @@ void vtime_guest_exit(struct task_struct *tsk)
current->flags &= ~PF_VCPU;
write_sequnlock(&tsk->vtime_seqlock);
}
+EXPORT_SYMBOL_GPL(vtime_guest_exit);
void vtime_account_idle(struct task_struct *tsk)
{
@@ -733,11 +717,6 @@ void vtime_account_idle(struct task_struct *tsk)
account_idle_time(delta_cpu);
}
-bool vtime_accounting_enabled(void)
-{
- return context_tracking_active();
-}
-
void arch_vtime_task_switch(struct task_struct *prev)
{
write_seqlock(&prev->vtime_seqlock);
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index 70f27e8..747bbc7 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -105,7 +105,6 @@ config NO_HZ_FULL
select RCU_USER_QS
select RCU_NOCB_CPU
select VIRT_CPU_ACCOUNTING_GEN
- select CONTEXT_TRACKING_FORCE
select IRQ_WORK
help
Adaptively try to shutdown the tick whenever possible, even when
diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
index a326f27..0b479a6 100644
--- a/kernel/time/sched_clock.c
+++ b/kernel/time/sched_clock.c
@@ -121,7 +121,7 @@ void __init setup_sched_clock(u32 (*read)(void), int bits, unsigned long rate)
BUG_ON(bits > 32);
WARN_ON(!irqs_disabled());
read_sched_clock = read;
- sched_clock_mask = (1 << bits) - 1;
+ sched_clock_mask = (1ULL << bits) - 1;
cd.rate = rate;
/* calculate the mult/shift to convert counter ticks to ns. */
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index e77edc9..adea6fc3 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -23,6 +23,7 @@
#include <linux/irq_work.h>
#include <linux/posix-timers.h>
#include <linux/perf_event.h>
+#include <linux/context_tracking.h>
#include <asm/irq_regs.h>
@@ -148,8 +149,8 @@ static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
}
#ifdef CONFIG_NO_HZ_FULL
-static cpumask_var_t nohz_full_mask;
-bool have_nohz_full_mask;
+cpumask_var_t tick_nohz_full_mask;
+bool tick_nohz_full_running;
static bool can_stop_full_tick(void)
{
@@ -182,7 +183,8 @@ static bool can_stop_full_tick(void)
* Don't allow the user to think they can get
* full NO_HZ with this machine.
*/
- WARN_ONCE(1, "NO_HZ FULL will not work with unstable sched clock");
+ WARN_ONCE(tick_nohz_full_running,
+ "NO_HZ FULL will not work with unstable sched clock");
return false;
}
#endif
@@ -196,7 +198,7 @@ static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now);
* Re-evaluate the need for the tick on the current CPU
* and restart it if necessary.
*/
-void tick_nohz_full_check(void)
+void __tick_nohz_full_check(void)
{
struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
@@ -210,7 +212,7 @@ void tick_nohz_full_check(void)
static void nohz_full_kick_work_func(struct irq_work *work)
{
- tick_nohz_full_check();
+ __tick_nohz_full_check();
}
static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
@@ -229,7 +231,7 @@ void tick_nohz_full_kick(void)
static void nohz_full_kick_ipi(void *info)
{
- tick_nohz_full_check();
+ __tick_nohz_full_check();
}
/*
@@ -238,11 +240,11 @@ static void nohz_full_kick_ipi(void *info)
*/
void tick_nohz_full_kick_all(void)
{
- if (!have_nohz_full_mask)
+ if (!tick_nohz_full_running)
return;
preempt_disable();
- smp_call_function_many(nohz_full_mask,
+ smp_call_function_many(tick_nohz_full_mask,
nohz_full_kick_ipi, NULL, false);
preempt_enable();
}
@@ -252,7 +254,7 @@ void tick_nohz_full_kick_all(void)
* It might need the tick due to per task/process properties:
* perf events, posix cpu timers, ...
*/
-void tick_nohz_task_switch(struct task_struct *tsk)
+void __tick_nohz_task_switch(struct task_struct *tsk)
{
unsigned long flags;
@@ -268,31 +270,23 @@ out:
local_irq_restore(flags);
}
-int tick_nohz_full_cpu(int cpu)
-{
- if (!have_nohz_full_mask)
- return 0;
-
- return cpumask_test_cpu(cpu, nohz_full_mask);
-}
-
/* Parse the boot-time nohz CPU list from the kernel parameters. */
static int __init tick_nohz_full_setup(char *str)
{
int cpu;
- alloc_bootmem_cpumask_var(&nohz_full_mask);
- if (cpulist_parse(str, nohz_full_mask) < 0) {
+ alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
+ if (cpulist_parse(str, tick_nohz_full_mask) < 0) {
pr_warning("NOHZ: Incorrect nohz_full cpumask\n");
return 1;
}
cpu = smp_processor_id();
- if (cpumask_test_cpu(cpu, nohz_full_mask)) {
+ if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
pr_warning("NO_HZ: Clearing %d from nohz_full range for timekeeping\n", cpu);
- cpumask_clear_cpu(cpu, nohz_full_mask);
+ cpumask_clear_cpu(cpu, tick_nohz_full_mask);
}
- have_nohz_full_mask = true;
+ tick_nohz_full_running = true;
return 1;
}
@@ -310,7 +304,7 @@ static int tick_nohz_cpu_down_callback(struct notifier_block *nfb,
* If we handle the timekeeping duty for full dynticks CPUs,
* we can't safely shutdown that CPU.
*/
- if (have_nohz_full_mask && tick_do_timer_cpu == cpu)
+ if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
return NOTIFY_BAD;
break;
}
@@ -329,14 +323,14 @@ static int tick_nohz_init_all(void)
int err = -1;
#ifdef CONFIG_NO_HZ_FULL_ALL
- if (!alloc_cpumask_var(&nohz_full_mask, GFP_KERNEL)) {
+ if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) {
pr_err("NO_HZ: Can't allocate full dynticks cpumask\n");
return err;
}
err = 0;
- cpumask_setall(nohz_full_mask);
- cpumask_clear_cpu(smp_processor_id(), nohz_full_mask);
- have_nohz_full_mask = true;
+ cpumask_setall(tick_nohz_full_mask);
+ cpumask_clear_cpu(smp_processor_id(), tick_nohz_full_mask);
+ tick_nohz_full_running = true;
#endif
return err;
}
@@ -345,17 +339,18 @@ void __init tick_nohz_init(void)
{
int cpu;
- if (!have_nohz_full_mask) {
+ if (!tick_nohz_full_running) {
if (tick_nohz_init_all() < 0)
return;
}
+ for_each_cpu(cpu, tick_nohz_full_mask)
+ context_tracking_cpu_set(cpu);
+
cpu_notifier(tick_nohz_cpu_down_callback, 0);
- cpulist_scnprintf(nohz_full_buf, sizeof(nohz_full_buf), nohz_full_mask);
+ cpulist_scnprintf(nohz_full_buf, sizeof(nohz_full_buf), tick_nohz_full_mask);
pr_info("NO_HZ: Full dynticks CPUs: %s.\n", nohz_full_buf);
}
-#else
-#define have_nohz_full_mask (0)
#endif
/*
@@ -733,7 +728,7 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
return false;
}
- if (have_nohz_full_mask) {
+ if (tick_nohz_full_enabled()) {
/*
* Keep the tick alive to guarantee timekeeping progression
* if there are full dynticks CPUs around
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