linux-kernel - Re: [PATCH] proc: Add RLIMIT_RTTIME to /proc/<pid>/limits

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Message-ID: <cfd18e0f0804110038q3b7740c9q1a96858d9531ab92@mail.gmail.com>
Date:	Fri, 11 Apr 2008 09:38:09 +0200
From:	"Michael Kerrisk" <mtk.manpages@...glemail.com>
To:	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>
Cc:	"Michael Kerrisk" <mtk.manpages@...il.com>,
	"Eugene Teo" <eugeneteo@...nel.sg>, linux-kernel@...r.kernel.org,
	"Neil Horman" <nhorman@...driver.com>,
	"Ingo Molnar" <mingo@...e.hu>
Subject: Re: [PATCH] proc: Add RLIMIT_RTTIME to /proc/<pid>/limits

On Thu, Feb 28, 2008 at 5:50 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
>
> On Thu, 2008-02-28 at 16:44 +0100, Michael Kerrisk wrote:
> > Peter,
> >
> > Thanks for the text.
> >
> > On Thu, Feb 28, 2008 at 4:21 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> > >
> > >  On Thu, 2008-02-28 at 16:12 +0100, Michael Kerrisk wrote:
> > >  > Peter,
> > >  >
> > >  > Could you please provide some text describing RLIMIT_RTTIMEfor the
> > >  > getrlimit.2 man page.
> > >
> > >  The rlimit sets a timeout in [us] for SCHED_RR and SCHED_FIFO tasks.
> > >  This time is measured between sleeps, so a schedule in RR or a
> > >  preemption in either is not a sleep - the task needs to be dequeued and
> > >  enqueued for the timer to reset.
> >
> > Just to clarify: sleep here means a call to some blocking syscall
> > (e.g., nanosleep(), read(), select(), etc.), right?  Is there anything
> > else that falls under the category of "sleep"?  What about a call to
> > sched_yield() where the process explicitly lets go of the CPU?
>
> Yes, and yes, others would be blocking on futexes and the like.

Peter,

I've been testing this patch.  Above you seemed to be saying that
doing a sched_yield() would be equivalent to a sleep, causing the rt
counter to be reset to zero.  Howver, the results I'm seeing suggest
that a sched_yield() does not cause the counter to be reset to zero
(i.e., despite calling sched_yield() at frequent intervals, the
process still encounters the RLIM_RTTIME soft limit and gets SIGXCPU).
 Can you comment?

Cheers,

Michael
-- 
Michael Kerrisk
Maintainer of the Linux man-pages project
http://www.kernel.org/doc/man-pages/
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