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author | Nick Piggin <nickpiggin@yahoo.com.au> | 2005-11-09 05:39:04 (GMT) |
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committer | Linus Torvalds <torvalds@g5.osdl.org> | 2005-11-09 15:56:33 (GMT) |
commit | 64c7c8f88559624abdbe12b5da6502e8879f8d28 (patch) | |
tree | 02f85a35ddd0f24dec70e5d6ecd61073578fd8d6 /arch/i386 | |
parent | 5bfb5d690f36d316a5f3b4f7775fda996faa6b12 (diff) | |
download | linux-fsl-qoriq-64c7c8f88559624abdbe12b5da6502e8879f8d28.tar.xz |
[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/i386')
-rw-r--r-- | arch/i386/kernel/apm.c | 20 | ||||
-rw-r--r-- | arch/i386/kernel/process.c | 64 |
2 files changed, 47 insertions, 37 deletions
diff --git a/arch/i386/kernel/apm.c b/arch/i386/kernel/apm.c index 86e80c5..003548b 100644 --- a/arch/i386/kernel/apm.c +++ b/arch/i386/kernel/apm.c @@ -769,8 +769,26 @@ static int set_system_power_state(u_short state) static int apm_do_idle(void) { u32 eax; + u8 ret = 0; + int idled = 0; + int polling; + + polling = test_thread_flag(TIF_POLLING_NRFLAG); + if (polling) { + clear_thread_flag(TIF_POLLING_NRFLAG); + smp_mb__after_clear_bit(); + } + if (!need_resched()) { + idled = 1; + ret = apm_bios_call_simple(APM_FUNC_IDLE, 0, 0, &eax); + } + if (polling) + set_thread_flag(TIF_POLLING_NRFLAG); + + if (!idled) + return 0; - if (apm_bios_call_simple(APM_FUNC_IDLE, 0, 0, &eax)) { + if (ret) { static unsigned long t; /* This always fails on some SMP boards running UP kernels. diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c index 5296e28..1cb261f 100644 --- a/arch/i386/kernel/process.c +++ b/arch/i386/kernel/process.c @@ -99,14 +99,22 @@ EXPORT_SYMBOL(enable_hlt); */ void default_idle(void) { + local_irq_enable(); + if (!hlt_counter && boot_cpu_data.hlt_works_ok) { - local_irq_disable(); - if (!need_resched()) - safe_halt(); - else - local_irq_enable(); + clear_thread_flag(TIF_POLLING_NRFLAG); + smp_mb__after_clear_bit(); + while (!need_resched()) { + local_irq_disable(); + if (!need_resched()) + safe_halt(); + else + local_irq_enable(); + } + set_thread_flag(TIF_POLLING_NRFLAG); } else { - cpu_relax(); + while (!need_resched()) + cpu_relax(); } } #ifdef CONFIG_APM_MODULE @@ -120,29 +128,14 @@ EXPORT_SYMBOL(default_idle); */ static void poll_idle (void) { - int oldval; - local_irq_enable(); - /* - * Deal with another CPU just having chosen a thread to - * run here: - */ - oldval = test_and_clear_thread_flag(TIF_NEED_RESCHED); - - if (!oldval) { - set_thread_flag(TIF_POLLING_NRFLAG); - asm volatile( - "2:" - "testl %0, %1;" - "rep; nop;" - "je 2b;" - : : "i"(_TIF_NEED_RESCHED), "m" (current_thread_info()->flags)); - - clear_thread_flag(TIF_POLLING_NRFLAG); - } else { - set_need_resched(); - } + asm volatile( + "2:" + "testl %0, %1;" + "rep; nop;" + "je 2b;" + : : "i"(_TIF_NEED_RESCHED), "m" (current_thread_info()->flags)); } #ifdef CONFIG_HOTPLUG_CPU @@ -181,6 +174,8 @@ void cpu_idle(void) { int cpu = smp_processor_id(); + set_thread_flag(TIF_POLLING_NRFLAG); + /* endless idle loop with no priority at all */ while (1) { while (!need_resched()) { @@ -246,15 +241,12 @@ static void mwait_idle(void) { local_irq_enable(); - if (!need_resched()) { - set_thread_flag(TIF_POLLING_NRFLAG); - do { - __monitor((void *)¤t_thread_info()->flags, 0, 0); - if (need_resched()) - break; - __mwait(0, 0); - } while (!need_resched()); - clear_thread_flag(TIF_POLLING_NRFLAG); + while (!need_resched()) { + __monitor((void *)¤t_thread_info()->flags, 0, 0); + smp_mb(); + if (need_resched()) + break; + __mwait(0, 0); } } |