linux/arch/alpha/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
..
Makefile Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
alpha_ksyms.c [PATCH] spinlock consolidation 2005-09-10 10:06:21 -07:00
asm-offsets.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
console.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
core_apecs.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
core_cia.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
core_irongate.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
core_lca.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
core_marvel.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
core_mcpcia.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
core_polaris.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
core_t2.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
core_titan.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
core_tsunami.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
core_wildfire.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
entry.S [PATCH] alpha: fix kernel alignment traps 2005-10-02 14:32:49 -07:00
err_common.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
err_ev6.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
err_ev7.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
err_impl.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
err_marvel.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
err_titan.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
es1888.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
gct.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
head.S kbuild: alpha,x86_64 use generic asm-offsets.h support 2005-09-09 21:28:48 +02:00
init_task.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
io.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
irq.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
irq_alpha.c [PATCH] alpha smp fix (part #2) 2005-07-01 08:20:23 -07:00
irq_i8259.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
irq_impl.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
irq_pyxis.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
irq_srm.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
machvec_impl.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
module.c [PATCH] alpha: process_reloc_for_got confuses r_offset and r_addend 2005-09-09 13:57:30 -07:00
ns87312.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
osf_sys.c [PATCH] files: fix preemption issues 2005-09-17 11:50:02 -07:00
pci-noop.c [PATCH] gfp_t: dma-mapping (alpha) 2005-10-28 08:16:48 -07:00
pci.c [PATCH] pci and yenta: pcibios_bus_to_resource 2005-08-04 21:32:46 -07:00
pci_impl.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
pci_iommu.c [PATCH] gfp_t: remaining bits of arch/* 2005-10-28 08:16:51 -07:00
process.c [PATCH] sched: resched and cpu_idle rework 2005-11-09 07:56:33 -08:00
proto.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
ptrace.c [PATCH] convert that currently tests _NSIG directly to use valid_signal() 2005-05-01 08:59:14 -07:00
semaphore.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
setup.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
signal.c [PATCH] convert signal handling of NODEFER to act like other Unix boxes. 2005-08-29 10:03:11 -07:00
smc37c93x.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
smc37c669.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
smp.c [PATCH] spinlock consolidation 2005-09-10 10:06:21 -07:00
srm_env.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
srmcons.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sys_alcor.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sys_cabriolet.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sys_dp264.c [PATCH] Alpha: ISA IRQs fixup for dp264 2005-09-19 10:00:59 -07:00
sys_eb64p.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sys_eiger.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sys_jensen.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sys_marvel.c [PATCH] PCI: remove CONFIG_PCI_NAMES 2005-09-08 14:57:23 -07:00
sys_miata.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sys_mikasa.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sys_nautilus.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sys_noritake.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sys_rawhide.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sys_ruffian.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sys_rx164.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sys_sable.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sys_sio.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sys_sx164.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sys_takara.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sys_titan.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sys_wildfire.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
systbls.S [PATCH] new alpha syscalls 2005-07-27 18:24:24 -07:00
time.c [PATCH] jiffies_64 cleanup 2005-10-30 17:37:25 -08:00
traps.c [PATCH] alpha: fix kernel alignment traps 2005-10-02 14:32:49 -07:00
vmlinux.lds.S Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00