Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932572Ab3IMOkZ (ORCPT ); Fri, 13 Sep 2013 10:40:25 -0400 Received: from merlin.infradead.org ([205.233.59.134]:54411 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932470Ab3IMOkX (ORCPT ); Fri, 13 Sep 2013 10:40:23 -0400 Date: Fri, 13 Sep 2013 16:40:08 +0200 From: Peter Zijlstra To: Christoph Lameter Cc: Frederic Weisbecker , Andrew Morton , Gilad Ben-Yossef , Thomas Gleixner , Mike Frysinger , linux-kernel@vger.kernel.org, "Paul E. McKenney" , Ingo Molnar Subject: Re: [RFC] Restrict kernel spawning of threads to a specified set of cpus. Message-ID: <20130913144008.GF21832@twins.programming.kicks-ass.net> References: <20130912141625.GA23357@somewhere> <00000141128d759a-44dcacb6-8f48-4f9b-8381-d14003bd6da1-000000@email.amazonses.com> <20130912143137.GA23839@somewhere> <0000014112a921ae-51d171bf-e8d4-4569-bd20-94dabda2d5ba-000000@email.amazonses.com> <20130912151102.GB23839@somewhere> <0000014112d66287-d0abaeb1-71ff-48a0-8740-f984d47400a7-000000@email.amazonses.com> <20130912183023.GA25386@somewhere> <20130913092553.GL31370@twins.programming.kicks-ass.net> <00000141179a5b1f-b94a8394-9e98-400c-ae7f-59cdcfce60a6-000000@email.amazonses.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <00000141179a5b1f-b94a8394-9e98-400c-ae7f-59cdcfce60a6-000000@email.amazonses.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1841 Lines: 41 On Fri, Sep 13, 2013 at 01:54:53PM +0000, Christoph Lameter wrote: > > > > If we really want to solve that race, then may be we can think of a kernel_parameter > > > > No bloody kernel params. I'd much rather create a pointless kthread to > > act as usermodehelper parent that people can set context on (move it > > into cgroups, set affinity, whatever) so it automagically propagates to > > all userspace helper thingies. > > > > Is there anything other than usermodehelper we need to be concerned > > with? One that comes to mind would be unbound workqueue threads. Do we > > want to share the parent with usermodehelpers or have these two classes > > have different parents? > > So you want to keep those silly racy move-all-threads-to-some-cpus scripts > around? No, creating a parent for them closes the race. It should also makes it lots easier to find the kids by using ppid. > A kernel parameter would allow a clean bootup with threads > starting out on the specific processors we want them to. Blergh, no. A kernel should boot, a kernel should allow you to configure things, a kernel should not be limited to boot time settings. > Also there is even more work ahead to deal with things like kswapd, > writeback threads, compaction and various other scanners that should also > be restricted. Mostly one thread per node is sufficient. This is not > simple to do from user space. IIRC we have one kswapd per node, not sure about the others. And why is this not simple from userspace? All these are long-running threads and from a quick look they can have their affinity changed. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/