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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/s390/kernel/process.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/s390/kernel/process.c')
-rw-r--r--arch/s390/kernel/process.c13
1 files changed, 7 insertions, 6 deletions
diff --git a/arch/s390/kernel/process.c b/arch/s390/kernel/process.c
index 66ca5757e368..78b64fe5e7c2 100644
--- a/arch/s390/kernel/process.c
+++ b/arch/s390/kernel/process.c
@@ -99,14 +99,15 @@ void default_idle(void)
99{ 99{
100 int cpu, rc; 100 int cpu, rc;
101 101
102 /* CPU is going idle. */
103 cpu = smp_processor_id();
104
102 local_irq_disable(); 105 local_irq_disable();
103 if (need_resched()) { 106 if (need_resched()) {
104 local_irq_enable(); 107 local_irq_enable();
105 return; 108 return;
106 } 109 }
107 110
108 /* CPU is going idle. */
109 cpu = smp_processor_id();
110 rc = notifier_call_chain(&idle_chain, CPU_IDLE, (void *)(long) cpu); 111 rc = notifier_call_chain(&idle_chain, CPU_IDLE, (void *)(long) cpu);
111 if (rc != NOTIFY_OK && rc != NOTIFY_DONE) 112 if (rc != NOTIFY_OK && rc != NOTIFY_DONE)
112 BUG(); 113 BUG();
@@ -119,7 +120,7 @@ void default_idle(void)
119 __ctl_set_bit(8, 15); 120 __ctl_set_bit(8, 15);
120 121
121#ifdef CONFIG_HOTPLUG_CPU 122#ifdef CONFIG_HOTPLUG_CPU
122 if (cpu_is_offline(smp_processor_id())) 123 if (cpu_is_offline(cpu))
123 cpu_die(); 124 cpu_die();
124#endif 125#endif
125 126