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sched: Call tick_check_idle before __irq_enter

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When CPU is idle and on first interrupt, irq_enter calls tick_check_idle()
to notify interruption from idle. But, there is a problem if this call
is done after __irq_enter, as all routines in __irq_enter may find
stale time due to yet to be done tick_check_idle.

Specifically, trace calls in __irq_enter when they use global clock and also
account_system_vtime change in this patch as it wants to use sched_clock_cpu()
to do proper irq timing.

But, tick_check_idle was moved after __irq_enter intentionally to
prevent problem of unneeded ksoftirqd wakeups by the commit ee5f80a:

    irq: call __irq_enter() before calling the tick_idle_check
    Impact: avoid spurious ksoftirqd wakeups

Moving tick_check_idle() before __irq_enter and wrapping it with
local_bh_enable/disable would solve both the problems.

Fixed-by: Yong Zhang <yong.zhang0@gmail.com>
Signed-off-by: Venkatesh Pallipadi <venki@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1286237003-12406-9-git-send-email-venki@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Venkatesh Pallipadi 2010-10-04 17:03:23 -07:00 committed by Ingo Molnar
parent aa48380851
commit d267f87fb8
2 changed files with 10 additions and 4 deletions
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2
kernel/sched.c
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@ -1974,8 +1974,8 @@ void account_system_vtime(struct task_struct *curr)
local_irq_save(flags); local_irq_save(flags);
now = sched_clock();
cpu = smp_processor_id(); cpu = smp_processor_id();
now = sched_clock_cpu(cpu);
delta = now - per_cpu(irq_start_time, cpu); delta = now - per_cpu(irq_start_time, cpu);
per_cpu(irq_start_time, cpu) = now; per_cpu(irq_start_time, cpu) = now;
/* /*

12
kernel/softirq.c
View File

@ -296,10 +296,16 @@ void irq_enter(void)
rcu_irq_enter(); rcu_irq_enter();
if (idle_cpu(cpu) && !in_interrupt()) { if (idle_cpu(cpu) && !in_interrupt()) {
__irq_enter(); /*
* Prevent raise_softirq from needlessly waking up ksoftirqd
* here, as softirq will be serviced on return from interrupt.
*/
local_bh_disable();
tick_check_idle(cpu); tick_check_idle(cpu);
} else _local_bh_enable();
__irq_enter(); }
__irq_enter();
} }
#ifdef __ARCH_IRQ_EXIT_IRQS_DISABLED #ifdef __ARCH_IRQ_EXIT_IRQS_DISABLED