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From: Peter Zijlstra <peterz@infradead.org>
To: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: linux-kernel@vger.kernel.org, andrea.parri@amarulasolutions.com
Subject: Re: Question about sched_setaffinity()
Date: Tue, 30 Apr 2019 13:55:51 +0200	[thread overview]
Message-ID: <20190430115551.GT2623@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190430105129.GA3923@linux.ibm.com>

On Tue, Apr 30, 2019 at 03:51:30AM -0700, Paul E. McKenney wrote:
> > Then I'm not entirely sure how we can return 0 and not run on the
> > expected CPU. If we look at __set_cpus_allowed_ptr(), the only paths out
> > to 0 are:
> > 
> >  - if the mask didn't change
> >  - if we already run inside the new mask
> >  - if we migrated ourself with the stop-task
> >  - if we're not in fact running
> > 
> > That last case should never trigger in your circumstances, since @p ==
> > current and current is obviously running. But for completeness, the
> > wakeup of @p would do the task placement in that case.
> 
> Are there some diagnostics I could add that would help track this down,
> be it my bug or yours?

Maybe limited function trace combined with the scheduling tracepoints
would give clue.

Trouble is, I forever forget how to set that up properly :/ Maybe
something along these lines:

$ trace-cmd record -p function_graph -g sched_setaffinity -g migration_cpu_stop -e
sched_migirate_task -e sched_switch -e sched_wakeup

Also useful would be:

echo 1 > /proc/sys/kernel/traceoff_on_warning

which ensures the trace stops the moment we find fail.

  reply	other threads:[~2019-04-30 11:55 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-27 18:02 Paul E. McKenney
2019-04-30 10:03 ` Peter Zijlstra
2019-04-30 10:51   ` Paul E. McKenney
2019-04-30 11:55     ` Peter Zijlstra [this message]
2019-05-01 19:12       ` Paul E. McKenney
2019-05-01 19:16         ` Steven Rostedt
2019-05-01 20:27           ` Paul E. McKenney
2019-05-07 22:16             ` Paul E. McKenney
2019-05-09 17:36               ` Paul E. McKenney
2019-05-09 19:36                 ` Paul E. McKenney
2019-05-10 12:08                   ` Peter Zijlstra
2019-05-10 23:07                     ` Paul E. McKenney
2019-05-11 21:45                       ` Andrea Parri
2019-05-12  0:39                         ` Paul E. McKenney
2019-05-12  1:05                           ` Andrea Parri
2019-05-13 12:20                             ` Paul E. McKenney
2019-05-13 15:37                               ` Joel Fernandes
2019-05-13 15:53                                 ` Paul E. McKenney
2019-05-13  8:10                       ` Peter Zijlstra
2019-05-13 12:19                         ` Paul E. McKenney
2019-05-09 21:40                 ` Andrea Parri
2019-05-09 21:56                   ` Andrea Parri
2019-05-09 22:17                     ` Paul E. McKenney
2019-05-10  6:32                       ` Andrea Parri

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