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

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Date:	Thu, 28 Feb 2008 16:50:21 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Michael Kerrisk <mtk.manpages@...glemail.com>
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, 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.

> Also, is this limit per-thread or per-process?  I assume the latter --
> but can you confirm please.

Per process. Requests have been made to allow for per thread, but
rlimits are not.

Its really not meant as a fine-grained deadline notification mechanism,
we have posix timers for that, but as a watchdog to ensure we behave
'well'.


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