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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: Fri, 08 Nov 2019 02:13:44 -0600	[thread overview]
Message-ID: <b56f988176fca4f13c310b9dc866baf5408eeadd.camel@redhat.com> (raw)
In-Reply-To: <20191105124351.GN4131@hirez.programming.kicks-ass.net>

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.

-Scott



  parent reply	other threads:[~2019-11-08  8:13 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 [this message]
2019-12-11 20:37                   ` Scott Wood
2019-12-11 20:46       ` Scott Wood

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