acrn-kernel/arch/parisc
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
..
configs [PARISC] defconfig updates 2005-10-21 23:11:03 -04:00
hpux kbuild: m68k,parisc,ppc,ppc64,s390,xtensa use generic asm-offsets.h support 2005-09-09 20:57:26 +02:00
kernel [PATCH] sched: resched and cpu_idle rework 2005-11-09 07:56:33 -08:00
lib [PARISC] Specify level to fix binutils level promotion bug 2005-10-21 22:56:35 -04:00
math-emu Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
mm [PATCH] memory hotplug locking: node_size_lock 2005-10-29 21:40:44 -07:00
oprofile Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
Kconfig [PARISC] Update Kconfig for itimer selection 2005-10-21 22:52:46 -04:00
Kconfig.debug Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
Makefile [PARISC] Update minimum compiler version and CROSS_COMPILE for parisc64 2005-10-21 22:52:00 -04:00
defconfig [PARISC] defconfig updates 2005-10-21 23:11:03 -04:00
defpalo.conf Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
install.sh Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
nm Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00