From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f69.google.com (mail-pg0-f69.google.com [74.125.83.69]) by kanga.kvack.org (Postfix) with ESMTP id 3E6E26B026F for ; Wed, 30 Nov 2016 12:02:57 -0500 (EST) Received: by mail-pg0-f69.google.com with SMTP id f188so36580599pgc.1 for ; Wed, 30 Nov 2016 09:02:57 -0800 (PST) Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com. [148.163.156.1]) by mx.google.com with ESMTPS id w17si65128498pgf.262.2016.11.30.09.02.56 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 30 Nov 2016 09:02:56 -0800 (PST) Received: from pps.filterd (m0098393.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.17/8.16.0.17) with SMTP id uAUGwixO083534 for ; Wed, 30 Nov 2016 12:02:55 -0500 Received: from e37.co.us.ibm.com (e37.co.us.ibm.com [32.97.110.158]) by mx0a-001b2d01.pphosted.com with ESMTP id 2721hk4cpd-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Wed, 30 Nov 2016 12:02:54 -0500 Received: from localhost by e37.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 30 Nov 2016 10:02:53 -0700 Date: Wed, 30 Nov 2016 09:02:49 -0800 From: "Paul E. McKenney" Subject: Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` Reply-To: paulmck@linux.vnet.ibm.com References: <20161124101525.GB20668@dhcp22.suse.cz> <583AA50A.9010608@molgen.mpg.de> <20161128110449.GK14788@dhcp22.suse.cz> <109d5128-f3a4-4b6e-db17-7a1fcb953500@molgen.mpg.de> <29196f89-c35e-f79d-8e4d-2bf73fe930df@molgen.mpg.de> <20161130110944.GD18432@dhcp22.suse.cz> <20161130115320.GO3924@linux.vnet.ibm.com> <20161130131910.GF18432@dhcp22.suse.cz> <20161130142955.GS3924@linux.vnet.ibm.com> <20161130163820.GQ3092@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161130163820.GQ3092@twins.programming.kicks-ass.net> Message-Id: <20161130170249.GZ3924@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Peter Zijlstra Cc: Michal Hocko , Donald Buczek , Paul Menzel , dvteam@molgen.mpg.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Josh Triplett On Wed, Nov 30, 2016 at 05:38:20PM +0100, Peter Zijlstra wrote: > On Wed, Nov 30, 2016 at 06:29:55AM -0800, Paul E. McKenney wrote: > > We can, and you are correct that cond_resched() does not unconditionally > > supply RCU quiescent states, and never has. Last time I tried to add > > cond_resched_rcu_qs() semantics to cond_resched(), I got told "no", > > but perhaps it is time to try again. > > Well, you got told: "ARRGH my benchmark goes all regress", or something > along those lines. Didn't we recently dig out those commits for some > reason or other? Were "those commits" the benchmark or putting cond_resched_rcu_qs() functionality into cond_resched()? Either way, no idea. > Finding out what benchmark that was and running it against this patch > would make sense. Agreed, especially given that I believe cond_resched_rcu_qs() is lighter weight than it used to be. No idea what benchmarks they were, though. > Also, I seem to have missed, why are we going through this again? People are running workloads that force long-running loops in the kernel, which get them RCU CPU stall warning messages. My reaction has been to insert cond_resched_rcu_qs() as needed, and Michal wondered why cond_resched() couldn't just handle both scheduling latency and RCU quiescent states. I remembered trying it, but not what the issue was. So I posted the patch assuming that I would eventually either find out what the issue was or that the issue no longer applied. ;-) Thanx, Paul -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org