From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751451AbeDEKJO (ORCPT ); Thu, 5 Apr 2018 06:09:14 -0400 Received: from mail-pl0-f50.google.com ([209.85.160.50]:39728 "EHLO mail-pl0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751104AbeDEKJM (ORCPT ); Thu, 5 Apr 2018 06:09:12 -0400 X-Google-Smtp-Source: AIpwx4+tAPMPcfsMEIvf3eIT8rwiSVll5o66xsAgnmtS/94NrdWAjWZ6Z4+2Kao1EMGUsYXh2NHVqA== Date: Thu, 5 Apr 2018 20:08:59 +1000 From: Nicholas Piggin To: Mike Galbraith Cc: Peter Zijlstra , Linux Kernel Mailing List , Steven Rostedt Subject: Re: sched_rt_period_timer causing large latencies Message-ID: <20180405200859.19fceb95@roar.ozlabs.ibm.com> In-Reply-To: <1522917620.5593.5.camel@gmx.de> References: <20180405091138.6ef14d15@roar.ozlabs.ibm.com> <20180405082701.GL4082@hirez.programming.kicks-ass.net> <1522917620.5593.5.camel@gmx.de> Organization: IBM X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; 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 Thu, 05 Apr 2018 10:40:20 +0200 Mike Galbraith wrote: > On Thu, 2018-04-05 at 10:27 +0200, Peter Zijlstra wrote: > > On Thu, Apr 05, 2018 at 09:11:38AM +1000, Nicholas Piggin wrote: > > > Hi, > > > > > > I'm seeing some pretty big latencies on a ~idle system when a CPU wakes > > > out of a nohz idle. Looks like it's due to the taking a lot of remote > > > locks and cache lines. irqoff trace: > > > > On RT I think we default RT_RUNTIME_SHARE to false, maybe we should do > > the same for mainline. > > Probably. My very first enterprise encounter with the thing was it NOT > saving a box from it's not so clever driver due to that. Well I would think a simpler per-cpu limiter might actually stand a better chance of saving you there. Or even something attached to the softlockup watchdog. I'm still getting a lot of locks coming from sched_rt_period_timer with RT_RUNTIME_SHARE false, it's just that it's now down to about NR_CPUS locks rather than 3*NR_CPUS. Thanks, Nick