From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761348Ab2DKV43 (ORCPT ); Wed, 11 Apr 2012 17:56:29 -0400 Received: from mail-we0-f174.google.com ([74.125.82.174]:51384 "EHLO mail-we0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756290Ab2DKV42 (ORCPT ); Wed, 11 Apr 2012 17:56:28 -0400 Message-ID: <4F85FE07.2060605@gmail.com> Date: Wed, 11 Apr 2012 23:56:23 +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: Steven Rostedt CC: peterz@infradead.org, tglx@linutronix.de, mingo@redhat.com, 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 08/16] sched: add period support for -deadline tasks. References: <1333696481-3433-1-git-send-email-juri.lelli@gmail.com> <1333696481-3433-9-git-send-email-juri.lelli@gmail.com> <1334176337.23924.297.camel@gandalf.stny.rr.com> In-Reply-To: <1334176337.23924.297.camel@gandalf.stny.rr.com> Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/11/2012 10:32 PM, Steven Rostedt wrote: > On Fri, 2012-04-06 at 09:14 +0200, Juri Lelli wrote: > >> @@ -293,7 +293,11 @@ static void replenish_dl_entity(struct sched_dl_entity *dl_se) >> * assigned (function returns true if it can). >> * >> * For this to hold, we must check if: >> - * runtime / (deadline - t)< dl_runtime / dl_deadline . >> + * runtime / (deadline - t)< dl_runtime / dl_period . >> + * >> + * Notice that the bandwidth check is done against the period. For >> + * task with deadline equal to period this is the same of using >> + * dl_deadline instead of dl_period in the equation above. > > First, it seems that the function returns true if: > > dl_runtime / dl_period< runtime / (deadline - t) > Right, the comment is wrong! Just reverse the inequality as you did. > > I'm a little confused by this. We are comparing the ratio of runtime > left and deadline left, to the ratio of total runtime to period. > > I'm actually confused by this premise anyway. What's the purpose of > comparing the ratio? If runtime< (deadline - t) wouldn't it not be able > to complete anyway? Or are we thinking that the runtime will be > interrupted proportionally by other tasks? > We are actually applying one of the CBS rules. We want to be able to "slow down" a deadline task if it is going to exceed its reserved bandwidth. We are in fact checking here that the bandwidth this task will consume from t to its deadline is no more than its reserved one. > > >> */ >> static bool dl_entity_overflow(struct sched_dl_entity *dl_se, u64 t) >> { >> @@ -312,7 +316,7 @@ static bool dl_entity_overflow(struct sched_dl_entity *dl_se, u64 t) >> * to the (absolute) deadline. Therefore, overflowing the u64 >> * type is very unlikely to occur in both cases. >> */ >> - left = dl_se->dl_deadline * dl_se->runtime; >> + left = dl_se->dl_period * dl_se->runtime; >> right = (dl_se->deadline - t) * dl_se->dl_runtime; >> >> return dl_time_before(right, left); > > Thanks, - Juri