linux/kernel
Nick Piggin 64c7c8f885 [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>
2005-11-09 07:56:33 -08:00
..
irq [PATCH] more kernel-doc cleanups, additions 2005-11-07 07:53:55 -08:00
power [PATCH] swsusp: rework swsusp_suspend 2005-11-09 07:55:52 -08:00
Kconfig.hz [PATCH] i386: Selectable Frequency of the Timer Interrupt 2005-06-23 09:45:10 -07:00
Kconfig.preempt [PATCH] sched: voluntary kernel preemption 2005-06-25 16:24:45 -07:00
Makefile [PATCH] RCU torture-testing kernel module 2005-10-30 17:37:27 -08:00
acct.c [PATCH] saner handling of auto_acct_off() and DQUOT_OFF() in umount 2005-11-07 18:18:09 -08:00
audit.c [PATCH] gfp_t: kernel/* 2005-10-28 08:16:49 -07:00
auditsc.c [PATCH] gfp_t: kernel/* 2005-10-28 08:16:49 -07:00
capability.c [PATCH] kernel/capability.c: add kerneldoc 2005-07-27 16:26:06 -07:00
compat.c [PATCH] kernel: fix-up schedule_timeout() usage 2005-09-10 10:06:37 -07:00
configs.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
cpu.c [PATCH] cpu hotplug: fix locking in cpufreq drivers 2005-11-09 07:55:50 -08:00
cpuset.c [PATCH] cpusets: automatic numa mempolicy rebinding 2005-10-30 17:37:22 -08:00
crash_dump.c [PATCH] kernel/crash_dump.c: add kerneldoc 2005-07-27 16:26:06 -07:00
dma.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
exec_domain.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
exit.c [PATCH] Process Events Connector 2005-11-07 07:53:35 -08:00
extable.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
fork.c [SPARC64] mm: context switch ptlock 2005-11-07 14:09:01 -08:00
futex.c [PATCH] FUTEX_WAKE_OP: enhanced error handling 2005-11-07 07:53:38 -08:00
intermodule.c [PATCH] introduce and use kzalloc 2005-09-07 16:57:45 -07:00
itimer.c [PATCH] itimer fixes 2005-07-27 16:25:51 -07:00
kallsyms.c [PATCH] fix missing includes 2005-10-30 17:37:32 -08:00
kexec.c [PATCH] mm: split page table lock 2005-10-29 21:40:42 -07:00
kfifo.c [PATCH] gfp flags annotations - part 1 2005-10-08 15:00:57 -07:00
kmod.c [PATCH] Keys: Get rid of warning in kmod.c if keys disabled 2005-10-30 17:37:23 -08:00
kprobes.c [PATCH] Kprobes: preempt_disable/enable() simplification 2005-11-07 07:53:46 -08:00
ksysfs.c [PATCH] Kdump: Export crash notes section address through sysfs 2005-06-25 16:24:51 -07:00
kthread.c [PATCH] Add kthread_stop_sem() 2005-10-30 17:37:17 -08:00
module.c [PATCH] fix remaining missing includes 2005-11-07 07:53:41 -08:00
panic.c [PATCH] Call emergency_reboot from panic 2005-07-26 14:35:43 -07:00
params.c [PATCH] fix missing includes 2005-10-30 17:37:32 -08:00
pid.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
posix-cpu-timers.c [PATCH] posix-timers `unlikely' rejig 2005-11-07 07:53:24 -08:00
posix-timers.c [PATCH] posix-timers: use schedule_timeout() in common_nsleep() 2005-10-30 17:37:20 -08:00
printk.c [PATCH] unexport console_unblank 2005-11-07 07:54:07 -08:00
profile.c [PATCH] mostly_read data section 2005-07-07 18:23:46 -07:00
ptrace.c [PATCH] consolidate sys_ptrace() 2005-11-07 07:53:42 -08:00
rcupdate.c [PATCH] RCU torture-testing kernel module 2005-10-30 17:37:27 -08:00
rcutorture.c [PATCH] RCU torture-testing kernel module 2005-10-30 17:37:27 -08:00
resource.c [PATCH] introduce and use kzalloc 2005-09-07 16:57:45 -07:00
sched.c [PATCH] sched: resched and cpu_idle rework 2005-11-09 07:56:33 -08:00
seccomp.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
signal.c [PATCH] Remove duplicate code in signal.c 2005-10-30 17:37:32 -08:00
softirq.c [PATCH] cpu hoptlug: avoid usage of smp_processor_id() in preemptible code 2005-11-07 07:53:29 -08:00
softlockup.c [PATCH] quieten softlockup at boot 2005-11-09 07:55:50 -08:00
spinlock.c [PATCH] spinlock consolidation 2005-09-10 10:06:21 -07:00
stop_machine.c [PATCH] smp_processor_id() cleanup 2005-06-21 18:46:13 -07:00
sys.c [PATCH] unexport uts_sem 2005-11-07 07:54:07 -08:00
sys_ni.c [PATCH] remove sys_set_zone_reclaim() 2005-08-01 10:03:56 -07:00
sysctl.c [PATCH] Fix sysctl unregistration oops (CVE-2005-2709) 2005-11-08 17:57:30 -08:00
time.c [PATCH] NTP shift_right cleanup 2005-10-30 17:37:18 -08:00
timer.c [PATCH] jiffies_64 cleanup 2005-10-30 17:37:25 -08:00
uid16.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
user.c [PATCH] inotify 2005-07-12 20:38:38 -07:00
wait.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
workqueue.c [PATCH] cpu hoptlug: avoid usage of smp_processor_id() in preemptible code 2005-11-07 07:53:29 -08:00