From: Scott Wood <swood@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Frederic Weisbecker <frederic@kernel.org>,
Ingo Molnar <mingo@kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] timers/nohz: Update nohz load even if tick already stopped
Date: Wed, 11 Dec 2019 14:37:05 -0600 [thread overview]
Message-ID: <e525584892b7f3a707ddfe32870e6128f888cefd.camel@redhat.com> (raw)
In-Reply-To: <b56f988176fca4f13c310b9dc866baf5408eeadd.camel@redhat.com>
On Fri, 2019-11-08 at 02:13 -0600, Scott Wood wrote:
> On Tue, 2019-11-05 at 13:43 +0100, Peter Zijlstra wrote:
> > On Tue, Nov 05, 2019 at 01:30:58AM -0600, Scott Wood wrote:
> > > As for the warning in sched_tick_remote(), it seems like a test for
> > > time
> > > since the last tick on this cpu (remote or otherwise) would be better
> > > than
> > > relying on curr->se.exec_start, in order to detect things like this.
> >
> > I don't think we have a timestamp that is shared between the remote and
> > local tick.
>
> Why wouldn't rq_clock_task() work on the local tick? It's what
> ->task_tick() itself uses.
>
> > Also, there is a reason this warning uses the task time
> > accounting, there used to be (as in, I can't find it in a hurry) code
> > that could not deal with >u32 (~4s) clock updates.
>
> Detecting a 3 second interval between ticks for a given cpu should
> assert in a superset of the situations the current check asserts in --
> it just avoids the false negative of exec_runtime getting updated by
> something other than the tick.
The main difficulty with such a check is that when we're not on a full
nohz cpu, there's no remote tick, and so we can legitimately go more than
3 seconds between ticks when idle.
-Scott
next prev parent reply other threads:[~2019-12-11 20:37 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-28 15:07 [PATCH] timers/nohz: Update nohz load even if tick already stopped Frederic Weisbecker
2019-10-29 10:05 ` Peter Zijlstra
2019-10-30 8:48 ` Scott Wood
2019-10-30 13:31 ` Peter Zijlstra
2019-11-01 5:11 ` Scott Wood
2019-11-04 22:17 ` Thomas Gleixner
2019-11-04 23:43 ` Thomas Gleixner
2019-11-05 7:30 ` Scott Wood
2019-11-05 9:53 ` Thomas Gleixner
2019-11-08 8:16 ` Scott Wood
2019-11-05 12:43 ` Peter Zijlstra
2019-11-06 8:37 ` Peter Zijlstra
2019-11-08 8:13 ` Scott Wood
2019-12-11 20:37 ` Scott Wood [this message]
2019-12-11 20:46 ` Scott Wood
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