Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754221Ab3ILPLJ (ORCPT ); Thu, 12 Sep 2013 11:11:09 -0400 Received: from mail-ee0-f50.google.com ([74.125.83.50]:50998 "EHLO mail-ee0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751461Ab3ILPLH (ORCPT ); Thu, 12 Sep 2013 11:11:07 -0400 Date: Thu, 12 Sep 2013 17:11:04 +0200 From: Frederic Weisbecker To: Christoph Lameter Cc: Andrew Morton , Gilad Ben-Yossef , Thomas Gleixner , Mike Frysinger , linux-kernel@vger.kernel.org, "Paul E. McKenney" Subject: Re: [RFC] Restrict kernel spawning of threads to a specified set of cpus. Message-ID: <20130912151102.GB23839@somewhere> References: <00000140efbcb701-c26320b3-f434-4538-bc80-8e92fed6f303-000000@email.amazonses.com> <20130911220228.GB15367@somewhere> <000001411282afa6-fe9c0543-0447-492b-991e-dc8214884b88-000000@email.amazonses.com> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0000014112a921ae-51d171bf-e8d4-4569-bd20-94dabda2d5ba-000000@email.amazonses.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1748 Lines: 38 On Thu, Sep 12, 2013 at 02:52:56PM +0000, Christoph Lameter wrote: > On Thu, 12 Sep 2013, Frederic Weisbecker wrote: > > > > > Ok but you can change the affinity of a kthread from userspace, as > > > > long as you define a cpu set that is among that kthread's cpus allowed. > > > > > > Ok but at that point kthread has already spawned a lot of kernel threads. > > > > > > The same is true for init and kmod. > > > > > > > Ok but then we just need to set the affinity of all these kthreads. > > A simple lookup on /proc/[0-9]+/ should do the trick. > > Yea but the kernel option makes it easy. No extras needed. Kernel brings > it up user space cleanly configured and ready to go. Ok but really that's just two lines of bash. I really wish we don't complicate core kernel code for that. I think we all agree that the big issue here is that CPU isolation requires to set up a fragmented set of features and it's not at all obvious to do it correctly: full dynticks, rcu nocbs, kthreads affinity, timer_list, hrtimers, workqueues, IPIs, etc... So IMHO what is missing is a reliable userspace tool that can handle all that: do the checks on pre-requirements, handle the kthreads and even user task affinity, tweak some sysctl stuffs to turn off features that generate noise, etc... > This also allows us to cleanup kernel uses of cpumasks in such a way that > proper thread placement for various other uses (reclaim f.e. kswpad) is > possible. Same here, a central tool should be able to solve that. -- 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/