linux/arch/powerpc/platforms/iseries
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
..
call_hpt.h merge filename and modify references to iseries/hv_types.h 2005-11-02 13:46:07 +11:00
call_pci.h merge filename and modify references to iseries/hv_types.h 2005-11-02 13:46:07 +11:00
call_sm.h merge filename and modify references to iseries/hv_types.h 2005-11-02 13:46:07 +11:00
htab.c [PATCH] ppc64: support 64k pages 2005-11-06 16:56:47 -08:00
hvcall.S powerpc: Get iseries to compile with ARCH=powerpc 2005-10-10 22:52:26 +10:00
hvlog.c [PATCH] ppc64: support 64k pages 2005-11-06 16:56:47 -08:00
hvlpconfig.c merge filename and modify reference to iseries/hv_lp_config.h 2005-11-02 11:55:28 +11:00
iommu.c [PATCH] ppc64: support 64k pages 2005-11-06 16:56:47 -08:00
ipl_parms.h ppc64 iseries: move some iSeries include files 2005-09-30 18:03:56 +10:00
irq.c [PATCH] powerpc: Kill ppcdebug 2005-11-07 12:37:45 +11:00
irq.h ppc64 iseries: move some iSeries include files 2005-09-30 18:03:56 +10:00
Kconfig powerpc: Merge enough to start building in arch/powerpc. 2005-09-26 16:04:21 +10:00
ksyms.c merge filename and modify references to iseries/hv_call_sc.h 2005-11-02 11:37:22 +11:00
lpardata.c Merge Paulus' tree 2005-11-02 18:15:43 +11:00
lpevents.c merge filename and modify references to iseries/it_lp_queue.h 2005-11-02 14:13:34 +11:00
main_store.h ppc64 iseries: move some iSeries include files 2005-09-30 18:03:56 +10:00
Makefile powerpc: make iSeries boot again 2005-10-12 10:58:00 +10:00
mf.c merge filename and modify references to iseries/vio.h 2005-11-02 15:13:57 +11:00
misc.S powerpc: move more iSeries code 2005-09-28 13:28:01 +10:00
naca.h [PATCH] powerpc: Move naca.h to platforms/iseries 2005-11-02 16:05:53 +11:00
pci.c [PATCH] powerpc: Kill ppcdebug 2005-11-07 12:37:45 +11:00
pci.h powerpc: eliminate DsaAddr from pci_dn 2005-10-14 16:49:58 +10:00
proc.c merge filename and modify references to iseries/it_lp_queue.h 2005-11-02 14:13:34 +11:00
processor_vpd.h ppc64 iseries: move some iSeries include files 2005-09-30 18:03:56 +10:00
release_data.h [PATCH] powerpc: Move naca.h to platforms/iseries 2005-11-02 16:05:53 +11:00
setup.c [PATCH] sched: resched and cpu_idle rework 2005-11-09 07:56:33 -08:00
setup.h powerpc: Merge machdep.h 2005-10-19 23:11:21 +10:00
smp.c [PATCH] powerpc: Kill ppcdebug 2005-11-07 12:37:45 +11:00
spcomm_area.h ppc64 iseries: move some iSeries include files 2005-09-30 18:03:56 +10:00
vio.c [PATCH] ppc64: support 64k pages 2005-11-06 16:56:47 -08:00
viopath.c [PATCH] ppc64: support 64k pages 2005-11-06 16:56:47 -08:00
vpd_areas.h ppc64 iseries: move some iSeries include files 2005-09-30 18:03:56 +10:00
vpdinfo.c merge filename and modify references to iseries/hv_types.h 2005-11-02 13:46:07 +11:00