From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mtk.manpages@gmail.com, Juri Lelli <juri.lelli@gmail.com>,
Dario Faggioli <raistlin@linux.it>, Ingo Molnar <mingo@elte.hu>,
lkml <linux-kernel@vger.kernel.org>,
Dave Jones <davej@redhat.com>
Subject: Re: [BUG] sched_setattr() SCHED_DEADLINE hangs system
Date: Mon, 12 May 2014 08:53:59 +0200 [thread overview]
Message-ID: <53707007.3080003@gmail.com> (raw)
In-Reply-To: <536F8F0E.7020301@gmail.com>
On 05/11/2014 04:54 PM, Michael Kerrisk (man-pages) wrote:
> [Dave: I wonder if there's anything trinity can add in the way of
> a test here?]
>
> Hi Peter,
>
> This looks like another bug in sched_setattr(). Using the program
> below (which you might find generally helpful for testing), I'm
> able to reliably freeze up my x64 (Intel Core i7-3520M Processor)
> system for up to about a minute when I run with the following
> command line:
>
> $ time sudo ./t_sched_setattr d 18446744072 18446744072 18446744073
>
> 'd' here means use SCHED_DEADLINE, then the remaining arguments
> are the Runtime, Deadline, and Period, expressed in *seconds*.
> (Those number by the way are just a little below 2^64.)
>
> Aside from interpreting its command-line arguments, all that the
> program does is call sched_setattr() and displays elapsed times.
> (By the way, on my system I see some weird effects for time(2),
> presumably VDSO effects.)
>
> Here's sample run:
>
> time sudo ./t_sched_setattr d 18446744072 18446744072 18446744073
> Runtime = 18446744072000000000
> Deadline = 18446744072000000000
> Period = 18446744073000000000
> About to call sched_setattr()
> Successful return from sched_setattr() [6 seconds]
>
> real 0m40.421s
> user 0m3.097s
> sys 0m30.804s
>
> After unfreezing the machine is fine, while the program is running,
> the machine is pretty unresponsive.
>
> I'm on kernel 3.15-rc4.
Hi Peter,
I realize my speculation was completely off the mark. time(2) really
is reporting the truth, and the sched_setattr() call returns immediately.
But it looks like with these settings the deadline scheduler gets itself
into a confused state. The process chews up a vast amount of CPU time
for the few actions (including process teardown) that occur after
the sched_setattr() call, and since the SCHED_DEADLINE process has
priority over everything else, the system locks up.
Cheers,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
next prev parent reply other threads:[~2014-05-12 6:54 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-11 14:54 [BUG] sched_setattr() SCHED_DEADLINE hangs system Michael Kerrisk (man-pages)
2014-05-11 17:47 ` Michael Kerrisk (man-pages)
2014-05-12 6:53 ` Michael Kerrisk (man-pages) [this message]
2014-05-12 8:47 ` Peter Zijlstra
2014-05-12 9:19 ` Michael Kerrisk (man-pages)
2014-05-12 12:30 ` Peter Zijlstra
2014-05-13 9:57 ` Juri Lelli
2014-05-13 10:43 ` Peter Zijlstra
2014-05-13 12:11 ` Juri Lelli
2014-05-13 12:46 ` Michael Kerrisk (man-pages)
2014-05-19 13:07 ` [tip:sched/core] sched/deadline: Restrict user params max value to 2^63 ns tip-bot for Juri Lelli
2014-05-22 12:25 ` tip-bot for Juri Lelli
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