Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757269AbbGGNed (ORCPT ); Tue, 7 Jul 2015 09:34:33 -0400 Received: from mail-wi0-f170.google.com ([209.85.212.170]:33396 "EHLO mail-wi0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754787AbbGGNeZ (ORCPT ); Tue, 7 Jul 2015 09:34:25 -0400 Date: Tue, 7 Jul 2015 15:34:22 +0200 From: Frederic Weisbecker To: Peter Zijlstra Cc: Fredrik =?iso-8859-1?Q?Markstr=F6m?= , mingo@redhat.com, linux-kernel@vger.kernel.org, Rik van Riel , Jason Low Subject: Re: [PATCH 1/1] cputime: Make the reported utime+stime correspond to the actual runtime. Message-ID: <20150707133420.GA20498@lerouge> References: <20150630093054.GK19282@twins.programming.kicks-ass.net> <20150630121812.GG3644@twins.programming.kicks-ass.net> <20150702121126.GP3644@twins.programming.kicks-ass.net> <20150702130701.GP18673@twins.programming.kicks-ass.net> <20150707005135.GH4981@lerouge> <20150707075954.GN3644@twins.programming.kicks-ass.net> <20150707080913.GT18673@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150707080913.GT18673@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1688 Lines: 48 On Tue, Jul 07, 2015 at 10:09:13AM +0200, Peter Zijlstra wrote: > On Tue, Jul 07, 2015 at 09:59:54AM +0200, Peter Zijlstra wrote: > > > > + /* > > > > + * Make sure stime doesn't go backwards; this preserves monotonicity > > > > + * for utime because rtime is monotonic. > > > > + * > > > > + * utime_i+1 = rtime_i+1 - stime_i > > > > + * = rtime_i+1 - (rtime_i - stime_i) > > > > + * = (rtime_i+1 - rtime_i) + stime_i > > > > + * >= stime_i > > > > + */ > > Argh, just noticed I messed that up, it should read: > > + /* > + * Make sure stime doesn't go backwards; this preserves monotonicity > + * for utime because rtime is monotonic. > + * > + * utime_i+1 = rtime_i+1 - stime_i > + * = rtime_i+1 - (rtime_i - utime_i) > + * = (rtime_i+1 - rtime_i) + utime_i > + * >= utime_i > + */ > > I got some [us] confusion. Typing is hard. > > So we compute: utime = rtime - stime, which we'll denote as: > > utime_i+1 = rtime_i+1 - stime_i But I don't get how you come to that. Imagine the following rounds: utime:2 stime:2 rtime:4 --> prev->utime = 2 prev->stime = 2 utime:2 stime:6 rtime:8 --> prev->utime = 2 prev->stime = 6 So here if I apply your above formula we have: utime_i+1:2 = rtime_i+1:8 - stime_i:2 Which doesn't work, so probably I still misunderstand those _i things... -- 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/