From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759747AbYDKJBk (ORCPT ); Fri, 11 Apr 2008 05:01:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757717AbYDKJBb (ORCPT ); Fri, 11 Apr 2008 05:01:31 -0400 Received: from viefep31-int.chello.at ([62.179.121.49]:53664 "EHLO viefep31-int.chello.at" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757997AbYDKJBb (ORCPT ); Fri, 11 Apr 2008 05:01:31 -0400 Subject: Re: [PATCH] proc: Add RLIMIT_RTTIME to /proc//limits From: Peter Zijlstra To: Michael Kerrisk Cc: Michael Kerrisk , Eugene Teo , linux-kernel@vger.kernel.org, Neil Horman , Ingo Molnar In-Reply-To: References: <20080208145950.GA3910@kernel.sg> <1202483445.6292.1.camel@lappy> <517f3f820802280712o3d756b4fq46461b226515e1f2@mail.gmail.com> <1204212100.12120.9.camel@twins> Content-Type: text/plain Date: Fri, 11 Apr 2008 11:01:25 +0200 Message-Id: <1207904485.7074.28.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.22.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.