From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932596AbcEQOdH (ORCPT ); Tue, 17 May 2016 10:33:07 -0400 Received: from smtprelay0016.hostedemail.com ([216.40.44.16]:50427 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932188AbcEQOdE (ORCPT ); Tue, 17 May 2016 10:33:04 -0400 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,rostedt@goodmis.org,:::::::,RULES_HIT:41:355:379:541:599:800:960:988:989:1260:1277:1311:1313:1314:1345:1359:1437:1515:1516:1518:1534:1540:1593:1594:1711:1730:1747:1777:1792:2393:2553:2559:2562:2693:3138:3139:3140:3141:3142:3352:3622:3865:3866:3867:3868:3871:3872:3874:4250:4605:5007:6119:6261:7875:7903:10004:10400:10848:10967:11232:11658:11914:12220:12517:12519:12740:13069:13311:13357:13439:14096:14097:14181:14659:14721:21063:21080:30054:30090:30091,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:none,Custom_rules:0:0:0,LFtime:4,LUA_SUMMARY:none X-HE-Tag: watch28_54a22fe71801b X-Filterd-Recvd-Size: 1847 Date: Tue, 17 May 2016 10:33:00 -0400 From: Steven Rostedt To: luca abeni Cc: Juri Lelli , LKML , Peter Zijlstra Subject: Re: Bug in AC? Message-ID: <20160517103300.2cf6e28e@gandalf.local.home> In-Reply-To: <20160517160749.39b0d880@utopia> References: <20160517090201.GA10196@pablo> <20160517123854.7204d206@utopia> <20160517094646.267f67dc@gandalf.local.home> <20160517160749.39b0d880@utopia> X-Mailer: Claws Mail 3.13.2 (GTK+ 2.24.30; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 17 May 2016 16:07:49 +0200 luca abeni wrote: > > As I > > mentioned on IRC, what about the case with two CPUs and this: > > > > Two tasks with: R:10us D: 15us P:100us > > and two tasks with: R:6us D: 14us P:14us > > > > If the period of the first two tasks line up on two different CPUs > > then there's no way the other two tasks will make their deadlines. > I agree this taskset is not schedulable on 2 CPUs. The problem is that > it is possible to generate tasksets with sum of densities < 2 that are > not schedulable on 2 CPUs. Makes sense. Thus the case is that we can't guarantee it on SMP anyway, so why put the extra effort to use deadline instead of period, where on UP we can make those guarantees. I was under the impression that it appeared everyone was saying that SMP we can guarantee it and UP we could not, which is where I was confused. -- Steve