Messages in this thread | | | Subject | Re: [PATCH] proc: Add RLIMIT_RTTIME to /proc/<pid>/limits | From | Peter Zijlstra <> | Date | Fri, 11 Apr 2008 11:32:05 +0200 |
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On Fri, 2008-04-11 at 11:27 +0200, Michael Kerrisk wrote: > On Fri, Apr 11, 2008 at 11:21 AM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: > > > > On Fri, 2008-04-11 at 11:16 +0200, Michael Kerrisk wrote: > > > 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? > > > > I'm not sure, nor will they actually work atm since its tick based. > > Just to make sure me and the man page are clear: by tick-based, you > mean the granularity is in jiffies, right?
Yes, they are currently jiffy based - but I could do hrtimer if someone shows need.
> > But > > I'm not wanting to exclude too many things, and 4k second upper limit is > > plenty large. > > Okay. > > And following on from my other conversation in this thread... What > should/will be the specified behavior w.r.t. resetting or not > resetting the timer on a sched_yield()?
I think I'll keep it as is; so sched_yield() will _not_ reset the counter. The rationale is that the process didn't actually stop running - it just got scheduled away.
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