linux-kernel - Re: [BUG] sched_setattr() SCHED

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Message-ID: <CAKgNAkiGt6xV0JaddmC8pLeTe+fSEu79DNvzg8XbA-MPo_zXyg@mail.gmail.com>
Date:	Mon, 12 May 2014 11:19:39 +0200
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Juri Lelli <juri.lelli@...il.com>,
	Dario Faggioli <raistlin@...ux.it>,
	Ingo Molnar <mingo@...e.hu>,
	lkml <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: [BUG] sched_setattr() SCHED_DEADLINE hangs system

Hi Peter,

On Mon, May 12, 2014 at 10:47 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, May 12, 2014 at 08:53:59AM +0200, Michael Kerrisk (man-pages) wrote:
>> On 05/11/2014 04:54 PM, Michael Kerrisk (man-pages) wrote:
>
>> > $ time sudo ./t_sched_setattr d 18446744072 18446744072 18446744073
>>
>> 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.
>
> Yeah, its doing something weird alright.. let me see if I can get
> something useful out.

Thanks!

> Btw, you do know about EX_USAGE from sysexits.h ?

Yes, I'm peripherally aware of them, but have tended to avoid them
because they're not in POSIX, and don't seem to be all that widely
used.

Cheers,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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