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author | Nick Piggin <nickpiggin@yahoo.com.au> | 2005-11-08 21:39:04 -0800 |
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committer | Linus Torvalds <torvalds@g5.osdl.org> | 2005-11-09 07:56:33 -0800 |
commit | 64c7c8f88559624abdbe12b5da6502e8879f8d28 (patch) | |
tree | 02f85a35ddd0f24dec70e5d6ecd61073578fd8d6 /arch/sparc/kernel | |
parent | 5bfb5d690f36d316a5f3b4f7775fda996faa6b12 (diff) | |
download | blackbird-op-linux-64c7c8f88559624abdbe12b5da6502e8879f8d28.tar.gz blackbird-op-linux-64c7c8f88559624abdbe12b5da6502e8879f8d28.zip |
[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>
Diffstat (limited to 'arch/sparc/kernel')
-rw-r--r-- | arch/sparc/kernel/process.c | 35 |
1 files changed, 15 insertions, 20 deletions
diff --git a/arch/sparc/kernel/process.c b/arch/sparc/kernel/process.c index c39f4d01096d..ea8647411462 100644 --- a/arch/sparc/kernel/process.c +++ b/arch/sparc/kernel/process.c @@ -67,13 +67,6 @@ extern void fpsave(unsigned long *, unsigned long *, void *, unsigned long *); struct task_struct *last_task_used_math = NULL; struct thread_info *current_set[NR_CPUS]; -/* - * default_idle is new in 2.5. XXX Review, currently stolen from sparc64. - */ -void default_idle(void) -{ -} - #ifndef CONFIG_SMP #define SUN4C_FAULT_HIGH 100 @@ -92,12 +85,11 @@ void cpu_idle(void) static unsigned long fps; unsigned long now; unsigned long faults; - unsigned long flags; extern unsigned long sun4c_kernel_faults; extern void sun4c_grow_kernel_ring(void); - local_irq_save(flags); + local_irq_disable(); now = jiffies; count -= (now - last_jiffies); last_jiffies = now; @@ -113,13 +105,16 @@ void cpu_idle(void) sun4c_grow_kernel_ring(); } } - local_irq_restore(flags); + local_irq_enable(); } - while((!need_resched()) && pm_idle) { - (*pm_idle)(); + if (pm_idle) { + while (!need_resched()) + (*pm_idle)(); + } else { + while (!need_resched()) + cpu_relax(); } - preempt_enable_no_resched(); schedule(); preempt_disable(); @@ -132,15 +127,15 @@ void cpu_idle(void) /* This is being executed in task 0 'user space'. */ void cpu_idle(void) { + set_thread_flag(TIF_POLLING_NRFLAG); /* endless idle loop with no priority at all */ while(1) { - if(need_resched()) { - preempt_enable_no_resched(); - schedule(); - preempt_disable(); - check_pgt_cache(); - } - barrier(); /* or else gcc optimizes... */ + while (!need_resched()) + cpu_relax(); + preempt_enable_no_resched(); + schedule(); + preempt_disable(); + check_pgt_cache(); } } |