From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753425Ab2LDW0e (ORCPT ); Tue, 4 Dec 2012 17:26:34 -0500 Received: from mx1.redhat.com ([209.132.183.28]:34941 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751836Ab2LDW0c (ORCPT ); Tue, 4 Dec 2012 17:26:32 -0500 From: Jeff Moyer To: Jens Axboe Cc: "linux-kernel\@vger.kernel.org" , "linux-mm\@kvack.org" , Zach Brown , tj@kernel.org, Peter Zijlstra , Ingo Subject: Re: [patch,v2] bdi: add a user-tunable cpu_list for the bdi flusher threads References: <50BE5988.3050501@fusionio.com> <50BE5C99.6070703@fusionio.com> X-PGP-KeyID: 1F78E1B4 X-PGP-CertKey: F6FE 280D 8293 F72C 65FD 5A58 1FF8 A7CA 1F78 E1B4 X-PCLoadLetter: What the f**k does that mean? Date: Tue, 04 Dec 2012 17:26:26 -0500 In-Reply-To: <50BE5C99.6070703@fusionio.com> (Jens Axboe's message of "Tue, 4 Dec 2012 21:27:05 +0100") Message-ID: User-Agent: Gnus/5.110011 (No Gnus v0.11) Emacs/23.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Jens Axboe writes: >>>> @@ -437,6 +488,14 @@ static int bdi_forker_thread(void *ptr) >>>> spin_lock_bh(&bdi->wb_lock); >>>> bdi->wb.task = task; >>>> spin_unlock_bh(&bdi->wb_lock); >>>> + mutex_lock(&bdi->flusher_cpumask_mutex); >>>> + ret = set_cpus_allowed_ptr(task, >>>> + bdi->flusher_cpumask); >>>> + mutex_unlock(&bdi->flusher_cpumask_mutex); >>> >>> It'd be very useful if we had a kthread_create_cpu_on_cpumask() instead >>> of a _node() variant, since the latter could easily be implemented on >>> top of the former. But not really a show stopper for the patch... >> >> Hmm, if it isn't too scary, I might give this a try. > > Should not be, pretty much just removing the node part of the create > struct passed in and making it a cpumask. And for the on_node() case, > cpumask_of_ndoe() will do the trick. I think it's a bit more involved than that. If you look at kthread_create_on_node, the node portion only applies to where the memory comes from, it says nothing of scheduling. To whit: /* * root may have changed our (kthreadd's) priority or CPU mask. * The kernel thread should not inherit these properties. */ sched_setscheduler_nocheck(create.result, SCHED_NORMAL, ¶m); set_cpus_allowed_ptr(create.result, cpu_all_mask); So, if I were to make the change you suggested, I would be modifying the existing behaviour. The way things stand, I think kthread_create_on_node violates the principal of least surprise. ;-) I would prefer a variant that affected scheduling behaviour as well as memory placement. Tejun, Peter, Ingo, what are your opinions? Cheers, Jeff