Re: [tip:sched/urgent] sched: Fix cross-cpu clock sync on remotewakeups

[Yong Zhang]

On Thu, Jun 02, 2011 at 03:04:26PM +0200, Peter Zijlstra wrote:
> On Thu, 2011-06-02 at 15:52 +0800, Yong Zhang wrote:
> > In sched_clock_local(), clock is calculated around ->tick_gtod even if
> > that ->tick_gtod is stale for long time because we stays in idle state. 
> > You know ->tick_gtod is only updated in sched_clock_tick();
> 
> (well, no, there's idle callbacks as you said below)
> 
> > IOW, when a cpu goes out of idle, sched_clock_tick() is called from
> > tick_nohz_stop_idle() which is later than interrupt.
> 
> Gah, that would be awefull and mean wakeups from interrupts were already
> borken. /me goes look at code.
> 
> irq_enter() -> tick_check_idle() -> tick_check_nohz() ->
> tick_nohz_stop_idle() -> sched_clock_idle_wakeup_event()
> 
> should update the thing before we run any isrs, right?

Hmmm, you are right.

But smp_reschedule_interrupt() doesn't call irq_enter()/irq_exit(),
is that correct?

Thanks,
Yong
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