Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933811AbcKGTRI (ORCPT ); Mon, 7 Nov 2016 14:17:08 -0500 Received: from smtprelay0159.hostedemail.com ([216.40.44.159]:54680 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S933149AbcKGTQ7 (ORCPT ); Mon, 7 Nov 2016 14:16:59 -0500 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,rostedt@goodmis.org,:::::::::::::,RULES_HIT:41:355:379:541:599:800:960:988:989:1260:1277:1311:1313:1314:1345:1359:1437:1515:1516:1518:1534:1541:1593:1594:1711:1730:1747:1777:1792:2393:2553:2559:2562:2692:2693:3138:3139:3140:3141:3142:3353:3622:3865:3866:3867:3868:3870:3871:3872:3873:3874:4250:5007:6261:7875:7903:9040:9389:10004:10400:10848:10967:11026:11232:11658:11914:12663:12740:12760:13069:13311:13357:13439:14096:14097:14181:14659:14721:21080:21324:30054:30090:30091,0,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:56,LUA_SUMMARY:none X-HE-Tag: print55_17cd9e4c08c00 X-Filterd-Recvd-Size: 2479 Date: Mon, 7 Nov 2016 14:16:02 -0500 From: Steven Rostedt To: Daniel Bristot de Oliveira Cc: Christoph Lameter , Daniel Bristot de Oliveira , Ingo Molnar , Peter Zijlstra , linux-rt-users , LKML Subject: Re: [PATCH] sched/rt: RT_RUNTIME_GREED sched feature Message-ID: <20161107141602.392952f0@gandalf.local.home> In-Reply-To: <47238aa4-cc41-96ac-4d6e-c182a340db85@bristot.me> References: <20161107133207.4282de69@gandalf.local.home> <47238aa4-cc41-96ac-4d6e-c182a340db85@bristot.me> X-Mailer: Claws Mail 3.14.0 (GTK+ 2.24.31; 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 Content-Length: 1252 Lines: 27 On Mon, 7 Nov 2016 19:49:03 +0100 Daniel Bristot de Oliveira wrote: > On 11/07/2016 07:32 PM, Steven Rostedt wrote: > >> Excellent this would improve the situation with deadlocks as a result of > >> > cgroup_locks not being released due to lack of workqueue processing. > > ?? What deadlocks do you see? I mean, can you show the situation that > > throttling RT tasks will cause deadlock? > > > > Sorry, but I'm just not seeing it. > > It is not a deadlock in the theoretical sense of the word, but it is > more a side effect of the starvation - that looks like a deadlock. > > There is a case where the removal of a cgroup dir calls > lru_add_drain_all(), that might schedule a kworker in the CPU that is > running the spinning-rt task. The kworker will starve - because they are > SCHED_OTHER by design, the lru_add_drain_all() will wait forever while > holding the cgroup lock and this will cause a lot of problems on other > tasks. I understand the issue with not throttling an RT task, but this patch is about not not throttling! That is, what scenario is there that will cause a "deadlock" or deadlock like to happen when we *do* throttle, where not throttling will work better, as this patch would have? -- Steve