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On 2006-11-09, Balbir Singh <balbir@in.ibm.com> wrote: > Path: news.gmane.org!not-for-mail> From: Balbir Singh <balbir@in.ibm.com>> Newsgroups: gmane.linux.kernel> Subject: Re: Jiffies wraparound is not treated in the schedstats > Date: Thu, 09 Nov 2006 11:59:45 +0530> Organization: IBM> Lines: 61> Approved: news@gmane.org> Message-ID: <4552CAD9.1080603@in.ibm.com>> References: <3f250c710611081005v5fcf3236qfb10b47bab1ada5f@mail.gmail.com> > Reply-To: balbir@in.ibm.com > NNTP-Posting-Host: main.gmane.org > Mime-Version: 1.0 > Content-Type: text/plain; charset=ISO-8859-1 > Content-Transfer-Encoding: 7bit > X-Trace: sea.gmane.org 1163053871 25652 80.91.229.2 (9 Nov 2006 06:31:11 GMT) > X-Complaints-To: usenet@sea.gmane.org > NNTP-Posting-Date: Thu, 9 Nov 2006 06:31:11 +0000 (UTC) > Cc: linux-kernel <linux-kernel@vger.kernel.org> > Original-X-From: linux-kernel-owner+glk-linux-kernel-3=40m.gmane.org-S1754746AbWKIGad@vger.kernel.org Thu Nov 09 07:31:09 2006 > Return-path: <linux-kernel-owner+glk-linux-kernel-3=40m.gmane.org-S1754746AbWKIGad@vger.kernel.org> > Envelope-to: glk-linux-kernel-3@gmane.org > Original-Received: from vger.kernel.org ([209.132.176.167]) by ciao.gmane.org with esmtp (Exim 4.43) id 1Gi3RH-0005lG-4D for glk-linux-kernel-3@gmane.org; Thu, 09 Nov 2006 07:31:03 +0100 > Original-Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754746AbWKIGad (ORCPT <rfc822;glk-linux-kernel-3@m.gmane.org>); Thu, 9 Nov 2006 01:30:33 -0500 > Original-Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754747AbWKIGad (ORCPT <rfc822;linux-kernel-outgoing>); Thu, 9 Nov 2006 01:30:33 -0500 > Original-Received: from ausmtp05.au.ibm.com ([202.81.18.154]:27366 "EHLO ausmtp05.au.ibm.com") by vger.kernel.org with ESMTP id S1754746AbWKIGac (ORCPT <rfc822;linux-kernel@vger.kernel.org>); Thu, 9 Nov 2006 01:30:32 -0500 > Original-Received: from sd0208e0.au.ibm.com (d23rh904.au.ibm.com [202.81.18.202]) by ausmtp05.au.ibm.com (8.13.8/8.13.6) with ESMTP id kA9IWR8m2142218 for <linux-kernel@vger.kernel.org>; Thu, 9 Nov 2006 17:32:29 -0100 > Original-Received: from d23av01.au.ibm.com (d23av01.au.ibm.com [9.190.250.242]) by sd0208e0.au.ibm.com (8.13.6/8.13.6/NCO v8.1.1) with ESMTP id kA96XQUu233974 for <linux-kernel@vger.kernel.org>; Thu, 9 Nov 2006 17:33:46 +1100 > Original-Received: from d23av01.au.ibm.com (loopback [127.0.0.1]) by d23av01.au.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id kA96TxcF020262 for <linux-kernel@vger.kernel.org>; Thu, 9 Nov 2006 17:29:59 +1100 > Original-Received: from [9.124.96.199] ([9.124.96.199]) by d23av01.au.ibm.com (8.12.11.20060308/8.12.11) with ESMTP id kA96Tuua020086; Thu, 9 Nov 2006 17:29:58 +1100 > User-Agent: Thunderbird 1.5.0.7 (X11/20060922) > Original-To: Mauricio Lin <mauriciolin@gmail.com> > In-Reply-To: <3f250c710611081005v5fcf3236qfb10b47bab1ada5f@mail.gmail.com> > Original-Sender: linux-kernel-owner@vger.kernel.org > Precedence: bulk > X-Mailing-List: linux-kernel@vger.kernel.org > Xref: news.gmane.org gmane.linux.kernel:465046 > Archived-At: <http://permalink.gmane.org/gmane.linux.kernel/465046> > > Mauricio Lin wrote: >> Hi Balbir,>> >> Do you know why in the sched_info_arrive() and sched_info_depart() >> functions the calculation of delta_jiffies does not use the time_after >> or time_before macro to prevent the miscalculation when jiffies >> overflow?>> >> For instance the delta_jiffies variable is simply calculated as: >> >> delta_jiffies = now - t->sched_info.last_queued; >> >> Do not you think the more logical way should be>> >> if (time_after(now, t->sched_info.last_queued))>> delta_jiffies = now - t->sched_info.last_queued; >> else >> delta_jiffies = (MAX_JIFFIES - t->sched_info.last_queued) + now >> > > What's MAX_JIFFIES? Is it MAX_ULONG? jiffies is unsigned long > so you'll have to be careful with unsigned long arithmetic. > > Consider that now is 5 and t->sched_info.last_queued is 10. > > On my system > > perl -e '{printf("%lu\n", -5 + (1<<32) - 1);}' > 4294967291 So, according to this > perl -e '{printf("%lu\n", -5 );}'> 4294967291 you have 32bit perl (and OS). I have same result in "This is perl, v5.8.4 built for i386-linux-thread-multi" (knoppix 3.2.3 in qemu on intel's amd64). That means we are on the same question i asked before about integer overflow. In this case "(1<<32) = 1", >> I have included more variables to measure some issues of schedule in >> the kernel (following schedstat idea) and I noticed that jiffies >> wraparound has led to wrong values, since the user space tool when >> collecting the values is producing negative values. >> >> hmm.. jiffies wrapped around in sched_info_depart()? I've never seen > that happen. Could you post the additions and user space tool to look at? > What additional features are you planning to measure in the scheduler? >>> Any comments?>> >> Can I provide a patch for that?>> >> Please feel free to provide patches, this is open source!! >>> BR,>> >> Mauricio Lin.>>> -- >> Balbir Singh, > Linux Technology Center, > IBM Software Labs - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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