From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755417Ab2DWNhO (ORCPT ); Mon, 23 Apr 2012 09:37:14 -0400 Received: from mail-bk0-f46.google.com ([209.85.214.46]:45287 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752454Ab2DWNhM (ORCPT ); Mon, 23 Apr 2012 09:37:12 -0400 Message-ID: <4F955B02.7040304@gmail.com> Date: Mon, 23 Apr 2012 15:37:06 +0200 From: Juri Lelli User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:11.0) Gecko/20120329 Thunderbird/11.0.1 MIME-Version: 1.0 To: Peter Zijlstra CC: tglx@linutronix.de, mingo@redhat.com, rostedt@goodmis.org, cfriesen@nortel.com, oleg@redhat.com, fweisbec@gmail.com, darren@dvhart.com, johan.eker@ericsson.com, p.faure@akatech.ch, linux-kernel@vger.kernel.org, claudio@evidence.eu.com, michael@amarulasolutions.com, fchecconi@gmail.com, tommaso.cucinotta@sssup.it, nicola.manica@disi.unitn.it, luca.abeni@unitn.it, dhaval.giani@gmail.com, hgu1972@gmail.com, paulmck@linux.vnet.ibm.com, raistlin@linux.it, insop.song@ericsson.com, liming.wang@windriver.com Subject: Re: [PATCH 05/16] sched: SCHED_DEADLINE policy implementation. References: <1333696481-3433-1-git-send-email-juri.lelli@gmail.com> <1333696481-3433-6-git-send-email-juri.lelli@gmail.com> <1335180743.28150.119.camel@twins> <4F954757.3020003@gmail.com> <1335183740.28150.135.camel@twins> In-Reply-To: <1335183740.28150.135.camel@twins> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/23/2012 02:22 PM, Peter Zijlstra wrote: > On Mon, 2012-04-23 at 14:13 +0200, Juri Lelli wrote: >> On 04/23/2012 01:32 PM, Peter Zijlstra wrote: >>> On Fri, 2012-04-06 at 09:14 +0200, Juri Lelli wrote: >>>> + /* >>>> + * We Keep moving the deadline away until we get some >>>> + * available runtime for the entity. This ensures correct >>>> + * handling of situations where the runtime overrun is >>>> + * arbitrary large. >>>> + */ >>>> + while (dl_se->runtime<= 0) { >>>> + dl_se->deadline += dl_se->dl_deadline; >>>> + dl_se->runtime += dl_se->dl_runtime; >>>> + } >>> >>> Does gcc 'optimize' that into a division? If so, it might need special >>> glue to make it not do that. >> >> I got two adds and a jle, no div here.. > > Gcc is known to change such loops to something like: > > if (runtime<= 0) { > tmp = 1 - runtime / dl_runtime; > deadline += tmp * dl_deadline; > runtime += tmp * dl_runtime; > } > > This is what I got for that snippet: ffffffff81062826 : [...] ffffffff81062885: 49 03 44 24 20 add 0x20(%r12),%rax ffffffff8106288a: 49 8b 54 24 28 mov 0x28(%r12),%rdx ffffffff8106288f: 49 01 54 24 38 add %rdx,0x38(%r12) ffffffff81062894: 49 89 44 24 30 mov %rax,0x30(%r12) ffffffff81062899: 49 8b 44 24 30 mov 0x30(%r12),%rax ffffffff8106289e: 48 85 c0 test %rax,%rax ffffffff810628a1: 7e e2 jle ffffffff81062885 So it seems we are fine in this case, right? It is anyway better to enforce this Gcc behaviour, just to be on the safe side? Thanks, - Juri