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From: "Michael Kerrisk" <mtk.manpages@googlemail.com>
To: "Peter Zijlstra" <a.p.zijlstra@chello.nl>
Cc: "Michael Kerrisk" <mtk.manpages@gmail.com>,
	"Eugene Teo" <eugeneteo@kernel.sg>,
	linux-kernel@vger.kernel.org,
	"Neil Horman" <nhorman@tuxdriver.com>,
	"Ingo Molnar" <mingo@elte.hu>
Subject: Re: [PATCH] proc: Add RLIMIT_RTTIME to /proc/<pid>/limits
Date: Fri, 11 Apr 2008 11:16:25 +0200	[thread overview]
Message-ID: <cfd18e0f0804110216l3c679bb6ned83f5d58d1c9d66@mail.gmail.com> (raw)
In-Reply-To: <1207904485.7074.28.camel@twins>

On Fri, Apr 11, 2008 at 11:01 AM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> On Fri, 2008-04-11 at 10:56 +0200, Michael Kerrisk wrote:
> > On Thu, Feb 28, 2008 at 5:21 PM, Peter Zijlstra <a.p.zijlstra@chello.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.
> > >
> > > Upon reaching the cur limit we start giving SIGXCPU every second, upon
> > > reaching the hard limit we give SIGKILL - matching RLIMIT_CPU.
> > >
> > > Time is measured in tick granularity (for now).
> >
> > So I have another question: why is the granularity of this rlimit
> > microseconds?  On the one hand, specifying limits down at the
> > microsecond level seems (to my naive eye) unlikely to be useful.  (But
> > perhaps I have missed a thread where this was explained.)  On the
> > other hand, it means that on 32-bit the largest time limit we can set
> > is ~4000 seconds, and I wonder if there are scenarios where it might
> > be useful to have larger limits than that.
> >
> > Why not, for example, have a granularity of milliseconds?
>
> The us scale seemed the best fit in that it allows sub-ms granularity
> while still allowing for quite long periods too. I'd preferred ns scale
> as that is what we use throughout the scheduler where possible - but
> that seemed too restrictive at the high end.
>
> No real hard arguments either way.

I'm curious: what scenarios require sub-millisecond timeouts?



-- 
Michael Kerrisk
Maintainer of the Linux man-pages project
http://www.kernel.org/doc/man-pages/
Want to report a man-pages bug? Look here:
http://www.kernel.org/doc/man-pages/reporting_bugs.html

  reply	other threads:[~2008-04-11  9:16 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-08 14:59 Eugene Teo
2008-02-08 15:10 ` Peter Zijlstra
2008-02-28 15:12   ` Michael Kerrisk
2008-02-28 15:21     ` Peter Zijlstra
2008-02-28 15:44       ` Michael Kerrisk
2008-02-28 15:50         ` Peter Zijlstra
2008-04-11  7:38           ` Michael Kerrisk
2008-04-11  7:45             ` Peter Zijlstra
2008-04-11  8:01               ` Michael Kerrisk
2008-02-29 12:32       ` Neil Horman
2008-04-11  8:56       ` Michael Kerrisk
2008-04-11  9:01         ` Peter Zijlstra
2008-04-11  9:16           ` Michael Kerrisk [this message]
2008-04-11  9:21             ` Peter Zijlstra
2008-04-11  9:27               ` Michael Kerrisk
2008-04-11  9:32                 ` Peter Zijlstra
2008-04-11  9:38                   ` Michael Kerrisk
2008-04-18 16:52                     ` RLIMIT_RTTIME documentation for getrlimit.2 Michael Kerrisk
2008-04-28 11:44                       ` Michael Kerrisk
2008-04-28 12:09                         ` Peter Zijlstra
2008-04-28 12:14                           ` Michael Kerrisk

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