From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Yong Zhang <yong.zhang0@gmail.com>
Cc: Borislav Petkov <bp@amd64.org>, Borislav Petkov <bp@alien8.de>,
"mingo@redhat.com" <mingo@redhat.com>,
"hpa@zytor.com" <hpa@zytor.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"markus@trippelsdorf.de" <markus@trippelsdorf.de>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"mingo@elte.hu" <mingo@elte.hu>,
"linux-tip-commits@vger.kernel.org"
<linux-tip-commits@vger.kernel.org>
Subject: Re: [tip:sched/urgent] sched: Fix cross-cpu clock sync on remote wakeups
Date: Thu, 02 Jun 2011 15:04:26 +0200 [thread overview]
Message-ID: <1307019866.2497.675.camel@laptop> (raw)
In-Reply-To: <BANLkTikT6OT-HDi-DR+_ZWEhfp_CYWJ3Hg@mail.gmail.com>
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?
> So if we have any site which call sched_clock() in interrupt on an
> idle cpu, it could get incorrect clock.
>
> I'm not sure how to teach sched_clock() about this special case, Peter?
isn't anything to teach afaict.
next prev parent reply other threads:[~2011-06-02 13:01 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-30 17:39 Very high CPU values in top on idle system (3.0-rc1) Markus Trippelsdorf
2011-05-30 18:05 ` Peter Zijlstra
2011-05-30 18:23 ` Markus Trippelsdorf
2011-05-30 20:45 ` Markus Trippelsdorf
2011-05-30 22:12 ` Peter Zijlstra
2011-05-31 9:55 ` Peter Zijlstra
2011-05-31 10:04 ` Markus Trippelsdorf
2011-05-31 12:31 ` [tip:sched/urgent] sched: Fix cross-cpu clock sync on remote wakeups tip-bot for Peter Zijlstra
2011-05-31 12:56 ` Borislav Petkov
2011-05-31 13:11 ` Peter Zijlstra
2011-06-01 7:05 ` Borislav Petkov
2011-06-01 10:36 ` Peter Zijlstra
2011-06-01 15:50 ` Borislav Petkov
2011-06-02 7:52 ` Yong Zhang
2011-06-02 13:04 ` Peter Zijlstra [this message]
2011-06-02 14:23 ` Yong Zhang
2011-06-02 15:48 ` Peter Zijlstra
2011-06-03 6:49 ` Yong Zhang
2011-06-07 13:12 ` Borislav Petkov
2011-06-07 13:16 ` Peter Zijlstra
2011-06-03 9:57 ` Milton Miller
2011-06-03 10:36 ` Peter Zijlstra
2011-06-03 10:55 ` Peter Zijlstra
2011-06-03 10:58 ` Peter Zijlstra
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