From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753644AbbDTRsL (ORCPT ); Mon, 20 Apr 2015 13:48:11 -0400 Received: from smtprelay0245.hostedemail.com ([216.40.44.245]:54033 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752175AbbDTRsI (ORCPT ); Mon, 20 Apr 2015 13:48:08 -0400 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,rostedt@goodmis.org,:::::::::,RULES_HIT:41:355:379:541:599:800:960:973:988:989:1260:1277:1311:1313:1314:1345:1359:1437:1515:1516:1518:1534:1541:1593:1594:1711:1730:1747:1777:1792:2198:2199:2393:2553:2559:2562:2731:3138:3139:3140:3141:3142:3353:3622:3865:3866:3867:3868:3870:3871:3872:3873:3874:4250:5007:6120:6261:6691:7875:7901:10004:10400:10848:10967:11026:11232:11658:11914:12043:12296:12438:12517:12519:12740:13069:13255:13311:13357:14096:14097:21080,0,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 X-HE-Tag: duck18_c59327dda729 X-Filterd-Recvd-Size: 2246 Date: Mon, 20 Apr 2015 13:48:03 -0400 From: Steven Rostedt To: Peter Zijlstra Cc: Xunlei Pang , linux-kernel@vger.kernel.org, Juri Lelli , Xunlei Pang Subject: Re: [PATCH v6 2/3] sched/rt: Fix wrong SMP scheduler behavior for equal prio cases Message-ID: <20150420134803.5446e32d@gandalf.local.home> In-Reply-To: <20150420172048.GZ27490@worktop.programming.kicks-ass.net> References: <1429518168-7965-1-git-send-email-xlpang@126.com> <1429518168-7965-2-git-send-email-xlpang@126.com> <20150420105228.461e103c@gandalf.local.home> <20150420172048.GZ27490@worktop.programming.kicks-ass.net> X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.25; 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 Mon, 20 Apr 2015 19:20:48 +0200 Peter Zijlstra wrote: > > > + */ > > > + if (preempt_count() & PREEMPT_ACTIVE) > > > + enqueue_pushable_task_preempted(rq, p); > > > + else > > > + enqueue_pushable_task(rq, p); > > > + } > > > } > > This looks wrong, what do you want to find? _any_ preemption? In that > case PREEMPT_ACTIVE is wrong. What you need to check is if the task is > still on the RQ or not. > > If the task was put to sleep it got dequeued, if it was not dequeued, it > got preempted. > > PREEMPT_ACTIVE is only ever set for forced kernel preemption, which is a > special sub case only ever triggered with CONFIG_PREEMPT=y. Ah, you're right. I was thinking of just forced preemption, but, I wasn't thinking about voluntary preemption (preemption points). We want this behavior for that too (for kernel). And yes, if we preempt in user space, this isn't enough either. Actually, I think we only care if the state of the task is TASK_RUNNING, if it is anything else, the task is probably going to sleep anyway and we don't care about FIFO order then. -- Steve