From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759901AbYDKJ2P (ORCPT ); Fri, 11 Apr 2008 05:28:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758441AbYDKJ2A (ORCPT ); Fri, 11 Apr 2008 05:28:00 -0400 Received: from wa-out-1112.google.com ([209.85.146.179]:22189 "EHLO wa-out-1112.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758251AbYDKJ17 (ORCPT ); Fri, 11 Apr 2008 05:27:59 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=googlemail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=TGC4PxVtMVuK0q1+ZbTD1N0Mf3PIPuCe1I9AR3LpoWaRp5aMS6C7XB/QeV8CaPWclUtgAjPdzOT6Qfk1W42I23DMIW0mdKI5J5dD69P0PtInufpxuUVgP44fgPOg3MoDE1koezxtTtvoDnAxKyQM3LqBBxSE3etLeX2JwHEHJIc= Message-ID: Date: Fri, 11 Apr 2008 11:27:59 +0200 From: "Michael Kerrisk" To: "Peter Zijlstra" Subject: Re: [PATCH] proc: Add RLIMIT_RTTIME to /proc//limits Cc: "Michael Kerrisk" , "Eugene Teo" , linux-kernel@vger.kernel.org, "Neil Horman" , "Ingo Molnar" In-Reply-To: <1207905668.7074.32.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <20080208145950.GA3910@kernel.sg> <1202483445.6292.1.camel@lappy> <517f3f820802280712o3d756b4fq46461b226515e1f2@mail.gmail.com> <1204212100.12120.9.camel@twins> <1207904485.7074.28.camel@twins> <1207905668.7074.32.camel@twins> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 11, 2008 at 11:21 AM, Peter Zijlstra wrote: > > On Fri, 2008-04-11 at 11:16 +0200, Michael Kerrisk wrote: > > On Fri, Apr 11, 2008 at 11:01 AM, Peter Zijlstra wrote: > > > On Fri, 2008-04-11 at 10:56 +0200, Michael Kerrisk wrote: > > > > On Thu, Feb 28, 2008 at 5:21 PM, Peter Zijlstra 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? > 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()? Cheers, Michael -- 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