From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933203AbcFJQLY (ORCPT ); Fri, 10 Jun 2016 12:11:24 -0400 Received: from smtprelay0050.hostedemail.com ([216.40.44.50]:34089 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752963AbcFJQLX (ORCPT ); Fri, 10 Jun 2016 12:11:23 -0400 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,rostedt@goodmis.org,:::::::::::::::::::,RULES_HIT:41:355:379:541:599:800:960:973:988:989:1260:1277:1311:1313:1314:1345:1359:1437:1515:1516:1518:1534:1541:1593:1594:1711:1730:1747:1777:1792:2393:2553:2559:2562:2693:3138:3139:3140:3141:3142:3353:3622:3865:3866:3867:3868:3870:3871:3872:3873:3874:4250:4321:5007:6261:7576:7875:7903:9545:10004:10400:10848:10967:11026:11232:11658:11914:12043:12296:12438:12517:12519:12663:12740:13069:13311:13357:13439:13868:13869:14096:14097:14181:14659:14721:21080:21433:30005:30054:30070:30090:30091,0,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:2,LUA_SUMMARY:none X-HE-Tag: look46_ba940e6aec22 X-Filterd-Recvd-Size: 2689 Date: Fri, 10 Jun 2016 12:11:18 -0400 From: Steven Rostedt To: Sebastian Andrzej Siewior Cc: alison@peloton-tech.com, LKML , linux-rt-users , netdev , Thomas Gleixner , Peter Zijlstra , Clark Williams , Eric Dumazet , David Miller Subject: Re: [PATCH][RT] netpoll: Always take poll_lock when doing polling Message-ID: <20160610121118.03f281e8@gandalf.local.home> In-Reply-To: <20160610155717.GB10775@linutronix.de> References: <20160526195641.6c26e979@gandalf.local.home> <20160602161235.GA12971@linutronix.de> <20160604071131.08d449db@grimm.local.home> <20160610155717.GB10775@linutronix.de> 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 Fri, 10 Jun 2016 17:57:17 +0200 Sebastian Andrzej Siewior wrote: > * Steven Rostedt | 2016-06-04 07:11:31 [-0400]: > > >From: Steven Rostedt > >Date: Tue, 5 Jan 2016 14:53:09 -0500 > >Subject: [PATCH] softirq: Perform softirqs in local_bh_enable() for a limited > > amount of time > > > >To prevent starvation of tasks like ksoftirqd, if the task that is > >processing its softirqs takes more than 2 jiffies to do so, and the > >softirqs are constantly being re-added, then defer the processing to > >ksoftirqd. > > I'm not sure about this. Alison didn't scream "yes it solves my problem" > and I am not sure what it is. > It is true that in RT we don't have such a limit like in !RT. You would > need to use __raise_softirq_irqoff_ksoft() instead the normal or + > wakeup() since you may have timers pending and those need to go to the > "other" ksoftirqd. > But then I don't see much change. ksoftirqd runs now at SCHED_OTHER so > it will end up on the CPU right away unless there other tasks that need > the CPU. So the scheduler will balance it the same way. The only change > will be that softirqs which are processed in context of any application > for more than two jiffies will be moved to ksoftirqd. This could be a > win. We actually triggered a starvation due to this. I was just seeing if Alison hit the same issue we did in our tests. -- Steve