From 64c7c8f88559624abdbe12b5da6502e8879f8d28 Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Tue, 8 Nov 2005 21:39:04 -0800 Subject: [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 Cc: Ingo Molnar Cc: Con Kolivas Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/sparc/kernel/process.c | 35 +++++++++++++++-------------------- 1 file changed, 15 insertions(+), 20 deletions(-) (limited to 'arch/sparc') diff --git a/arch/sparc/kernel/process.c b/arch/sparc/kernel/process.c index c39f4d0..ea86474 100644 --- a/arch/sparc/kernel/process.c +++ b/arch/sparc/kernel/process.c @@ -67,13 +67,6 @@ extern void fpsave(unsigned long *, unsigned long *, void *, unsigned long *); struct task_struct *last_task_used_math = NULL; struct thread_info *current_set[NR_CPUS]; -/* - * default_idle is new in 2.5. XXX Review, currently stolen from sparc64. - */ -void default_idle(void) -{ -} - #ifndef CONFIG_SMP #define SUN4C_FAULT_HIGH 100 @@ -92,12 +85,11 @@ void cpu_idle(void) static unsigned long fps; unsigned long now; unsigned long faults; - unsigned long flags; extern unsigned long sun4c_kernel_faults; extern void sun4c_grow_kernel_ring(void); - local_irq_save(flags); + local_irq_disable(); now = jiffies; count -= (now - last_jiffies); last_jiffies = now; @@ -113,13 +105,16 @@ void cpu_idle(void) sun4c_grow_kernel_ring(); } } - local_irq_restore(flags); + local_irq_enable(); } - while((!need_resched()) && pm_idle) { - (*pm_idle)(); + if (pm_idle) { + while (!need_resched()) + (*pm_idle)(); + } else { + while (!need_resched()) + cpu_relax(); } - preempt_enable_no_resched(); schedule(); preempt_disable(); @@ -132,15 +127,15 @@ void cpu_idle(void) /* This is being executed in task 0 'user space'. */ void cpu_idle(void) { + set_thread_flag(TIF_POLLING_NRFLAG); /* endless idle loop with no priority at all */ while(1) { - if(need_resched()) { - preempt_enable_no_resched(); - schedule(); - preempt_disable(); - check_pgt_cache(); - } - barrier(); /* or else gcc optimizes... */ + while (!need_resched()) + cpu_relax(); + preempt_enable_no_resched(); + schedule(); + preempt_disable(); + check_pgt_cache(); } } -- cgit v1.1