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

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Date:	Fri, 11 Apr 2008 10:56:49 +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 5:21 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.
>
> 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?

Cheers,

Michael


> > On Fri, Feb 8, 2008 at 4:10 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> > >
> > > On Fri, 2008-02-08 at 22:59 +0800, Eugene Teo wrote:
> > > > RLIMIT_RTTIME was introduced to allow the user to set a runtime timeout on
> > > > real-time tasks: http://lkml.org/lkml/2007/12/18/218. This patch updates
> > > > /proc/<pid>/limits with the new rlimit.
> > >
> > > Ah, didn't know about that file, thanks!
> > >
> > > > Signed-off-by: Eugene Teo <eugeneteo@...nel.sg>
> > >
> > > Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > >
> > >
> > > > ---
> > > >  fs/proc/base.c |    1 +
> > > >  1 files changed, 1 insertions(+), 0 deletions(-)
> > > >
> > > > diff --git a/fs/proc/base.c b/fs/proc/base.c
> > > > index c59852b..dcf7be8 100644
> > > > --- a/fs/proc/base.c
> > > > +++ b/fs/proc/base.c
> > > > @@ -412,6 +412,7 @@ static const struct limit_names lnames[RLIM_NLIMITS] = {
> > > >       [RLIMIT_MSGQUEUE] = {"Max msgqueue size", "bytes"},
> > > >       [RLIMIT_NICE] = {"Max nice priority", NULL},
> > > >       [RLIMIT_RTPRIO] = {"Max realtime priority", NULL},
> > > > +     [RLIMIT_RTTIME] = {"Max realtime timeout", "us"},
> > > >  };
> > > >
> > > >  /* Display limits for a process */
> > >
> > > --
> > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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> > > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > > Please read the FAQ at  http://www.tux.org/lkml/
> > >
> >
> >
> >
>
>



-- 
Michael Kerrisk
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