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Message-ID: <20110602142340.GA3356@zhy>
Date: Thu, 2 Jun 2011 22:23:40 +0800
From: Yong Zhang <yong.zhang0@...il.com>
To: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Borislav Petkov <bp@...64.org>, Borislav Petkov <bp@...en8.de>,
"mingo@...hat.com" <mingo@...hat.com>,
"hpa@...or.com" <hpa@...or.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"markus@...ppelsdorf.de" <markus@...ppelsdorf.de>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"mingo@...e.hu" <mingo@...e.hu>,
"linux-tip-commits@...r.kernel.org"
<linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:sched/urgent] sched: Fix cross-cpu clock sync on remote
wakeups
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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