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author | Nick Piggin <nickpiggin@yahoo.com.au> | 2005-11-08 21:39:04 -0800 |
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committer | Linus Torvalds <torvalds@g5.osdl.org> | 2005-11-09 07:56:33 -0800 |
commit | 64c7c8f88559624abdbe12b5da6502e8879f8d28 (patch) | |
tree | 02f85a35ddd0f24dec70e5d6ecd61073578fd8d6 /arch/ppc64/kernel | |
parent | 5bfb5d690f36d316a5f3b4f7775fda996faa6b12 (diff) | |
download | op-kernel-dev-64c7c8f88559624abdbe12b5da6502e8879f8d28.zip op-kernel-dev-64c7c8f88559624abdbe12b5da6502e8879f8d28.tar.gz |
[PATCH] sched: resched and cpu_idle rework
Make some changes to the NEED_RESCHED and POLLING_NRFLAG to reduce
confusion, and make their semantics rigid. Improves efficiency of
resched_task and some cpu_idle routines.
* In resched_task:
- TIF_NEED_RESCHED is only cleared with the task's runqueue lock held,
and as we hold it during resched_task, then there is no need for an
atomic test and set there. The only other time this should be set is
when the task's quantum expires, in the timer interrupt - this is
protected against because the rq lock is irq-safe.
- If TIF_NEED_RESCHED is set, then we don't need to do anything. It
won't get unset until the task get's schedule()d off.
- If we are running on the same CPU as the task we resched, then set
TIF_NEED_RESCHED and no further action is required.
- If we are running on another CPU, and TIF_POLLING_NRFLAG is *not* set
after TIF_NEED_RESCHED has been set, then we need to send an IPI.
Using these rules, we are able to remove the test and set operation in
resched_task, and make clear the previously vague semantics of
POLLING_NRFLAG.
* In idle routines:
- Enter cpu_idle with preempt disabled. When the need_resched() condition
becomes true, explicitly call schedule(). This makes things a bit clearer
(IMO), but haven't updated all architectures yet.
- Many do a test and clear of TIF_NEED_RESCHED for some reason. According
to the resched_task rules, this isn't needed (and actually breaks the
assumption that TIF_NEED_RESCHED is only cleared with the runqueue lock
held). So remove that. Generally one less locked memory op when switching
to the idle thread.
- Many idle routines clear TIF_POLLING_NRFLAG, and only set it in the inner
most polling idle loops. The above resched_task semantics allow it to be
set until before the last time need_resched() is checked before going into
a halt requiring interrupt wakeup.
Many idle routines simply never enter such a halt, and so POLLING_NRFLAG
can be always left set, completely eliminating resched IPIs when rescheduling
the idle task.
POLLING_NRFLAG width can be increased, to reduce the chance of resched IPIs.
Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Con Kolivas <kernel@kolivas.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'arch/ppc64/kernel')
-rw-r--r-- | arch/ppc64/kernel/idle.c | 11 |
1 files changed, 2 insertions, 9 deletions
diff --git a/arch/ppc64/kernel/idle.c b/arch/ppc64/kernel/idle.c index 909ea66..715bc0e 100644 --- a/arch/ppc64/kernel/idle.c +++ b/arch/ppc64/kernel/idle.c @@ -34,15 +34,11 @@ extern void power4_idle(void); void default_idle(void) { - long oldval; unsigned int cpu = smp_processor_id(); + set_thread_flag(TIF_POLLING_NRFLAG); while (1) { - oldval = test_and_clear_thread_flag(TIF_NEED_RESCHED); - - if (!oldval) { - set_thread_flag(TIF_POLLING_NRFLAG); - + if (!need_resched()) { while (!need_resched() && !cpu_is_offline(cpu)) { ppc64_runlatch_off(); @@ -55,9 +51,6 @@ void default_idle(void) } HMT_medium(); - clear_thread_flag(TIF_POLLING_NRFLAG); - } else { - set_need_resched(); } ppc64_runlatch_on(); |