diff options
author | Nick Piggin <nickpiggin@yahoo.com.au> | 2005-11-09 00:39:04 -0500 |
---|---|---|
committer | Linus Torvalds <torvalds@g5.osdl.org> | 2005-11-09 10:56:33 -0500 |
commit | 64c7c8f88559624abdbe12b5da6502e8879f8d28 (patch) | |
tree | 02f85a35ddd0f24dec70e5d6ecd61073578fd8d6 /arch/sparc64/kernel/smp.c | |
parent | 5bfb5d690f36d316a5f3b4f7775fda996faa6b12 (diff) |
[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/sparc64/kernel/smp.c')
-rw-r--r-- | arch/sparc64/kernel/smp.c | 13 |
1 files changed, 1 insertions, 12 deletions
diff --git a/arch/sparc64/kernel/smp.c b/arch/sparc64/kernel/smp.c index 8aca4b1dc04e..797a65493fb8 100644 --- a/arch/sparc64/kernel/smp.c +++ b/arch/sparc64/kernel/smp.c | |||
@@ -1152,20 +1152,9 @@ void __init smp_cpus_done(unsigned int max_cpus) | |||
1152 | (bogosum/(5000/HZ))%100); | 1152 | (bogosum/(5000/HZ))%100); |
1153 | } | 1153 | } |
1154 | 1154 | ||
1155 | /* This needn't do anything as we do not sleep the cpu | ||
1156 | * inside of the idler task, so an interrupt is not needed | ||
1157 | * to get a clean fast response. | ||
1158 | * | ||
1159 | * XXX Reverify this assumption... -DaveM | ||
1160 | * | ||
1161 | * Addendum: We do want it to do something for the signal | ||
1162 | * delivery case, we detect that by just seeing | ||
1163 | * if we are trying to send this to an idler or not. | ||
1164 | */ | ||
1165 | void smp_send_reschedule(int cpu) | 1155 | void smp_send_reschedule(int cpu) |
1166 | { | 1156 | { |
1167 | if (cpu_data(cpu).idle_volume == 0) | 1157 | smp_receive_signal(cpu); |
1168 | smp_receive_signal(cpu); | ||
1169 | } | 1158 | } |
1170 | 1159 | ||
1171 | /* This is a nop because we capture all other cpus | 1160 | /* This is a nop because we capture all other cpus |