64c7c8f885
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>
123 lines
2.5 KiB
C
123 lines
2.5 KiB
C
/*
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* Idle daemon for PowerPC. Idle daemon will handle any action
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* that needs to be taken when the system becomes idle.
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*
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* Originally Written by Cort Dougan (cort@cs.nmt.edu)
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*
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* iSeries supported added by Mike Corrigan <mikejc@us.ibm.com>
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*
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* Additional shared processor, SMT, and firmware support
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* Copyright (c) 2003 Dave Engebretsen <engebret@us.ibm.com>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#include <linux/config.h>
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#include <linux/sched.h>
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#include <linux/kernel.h>
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#include <linux/smp.h>
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#include <linux/cpu.h>
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#include <linux/sysctl.h>
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#include <asm/system.h>
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#include <asm/processor.h>
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#include <asm/cputable.h>
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#include <asm/time.h>
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#include <asm/systemcfg.h>
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#include <asm/machdep.h>
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#include <asm/smp.h>
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extern void power4_idle(void);
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void default_idle(void)
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{
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unsigned int cpu = smp_processor_id();
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set_thread_flag(TIF_POLLING_NRFLAG);
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while (1) {
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if (!need_resched()) {
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while (!need_resched() && !cpu_is_offline(cpu)) {
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ppc64_runlatch_off();
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/*
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* Go into low thread priority and possibly
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* low power mode.
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*/
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HMT_low();
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HMT_very_low();
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}
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HMT_medium();
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}
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ppc64_runlatch_on();
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preempt_enable_no_resched();
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schedule();
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preempt_disable();
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if (cpu_is_offline(cpu) && system_state == SYSTEM_RUNNING)
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cpu_die();
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}
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}
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void native_idle(void)
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{
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while (1) {
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ppc64_runlatch_off();
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if (!need_resched())
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power4_idle();
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if (need_resched()) {
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ppc64_runlatch_on();
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preempt_enable_no_resched();
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schedule();
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preempt_disable();
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}
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if (cpu_is_offline(smp_processor_id()) &&
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system_state == SYSTEM_RUNNING)
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cpu_die();
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}
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}
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void cpu_idle(void)
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{
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BUG_ON(NULL == ppc_md.idle_loop);
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ppc_md.idle_loop();
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}
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int powersave_nap;
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#ifdef CONFIG_SYSCTL
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/*
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* Register the sysctl to set/clear powersave_nap.
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*/
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static ctl_table powersave_nap_ctl_table[]={
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{
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.ctl_name = KERN_PPC_POWERSAVE_NAP,
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.procname = "powersave-nap",
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.data = &powersave_nap,
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.maxlen = sizeof(int),
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.mode = 0644,
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.proc_handler = &proc_dointvec,
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},
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{ 0, },
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};
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static ctl_table powersave_nap_sysctl_root[] = {
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{ 1, "kernel", NULL, 0, 0755, powersave_nap_ctl_table, },
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{ 0,},
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};
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static int __init
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register_powersave_nap_sysctl(void)
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{
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register_sysctl_table(powersave_nap_sysctl_root, 0);
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return 0;
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}
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__initcall(register_powersave_nap_sysctl);
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#endif
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