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authorNick Piggin <nickpiggin@yahoo.com.au>2005-11-09 00:39:04 -0500
committerLinus Torvalds <torvalds@g5.osdl.org>2005-11-09 10:56:33 -0500
commit64c7c8f88559624abdbe12b5da6502e8879f8d28 (patch)
tree02f85a35ddd0f24dec70e5d6ecd61073578fd8d6 /arch/sparc64/kernel/smp.c
parent5bfb5d690f36d316a5f3b4f7775fda996faa6b12 (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.c13
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 */
1165void smp_send_reschedule(int cpu) 1155void 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