Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755548Ab0GANay (ORCPT ); Thu, 1 Jul 2010 09:30:54 -0400 Received: from casper.infradead.org ([85.118.1.10]:52713 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754555Ab0GANaw convert rfc822-to-8bit (ORCPT ); Thu, 1 Jul 2010 09:30:52 -0400 Subject: Re: [PATCH repost] sched: export sched_set/getaffinity to modules From: Peter Zijlstra To: "Michael S. Tsirkin" Cc: Ingo Molnar , Sridhar Samudrala , Tejun Heo , Oleg Nesterov , netdev , lkml , "kvm@vger.kernel.org" , Andrew Morton , Dmitri Vorobiev , Jiri Kosina , Thomas Gleixner , Andi Kleen In-Reply-To: <20100701130816.GB32223@redhat.com> References: <20100624081135.GA937@redhat.com> <1277419551.27868.27.camel@w-sridhar.beaverton.ibm.com> <20100625101022.GA16321@redhat.com> <20100701110708.GA27368@redhat.com> <1277983179.1917.10.camel@laptop> <1277984603.1917.15.camel@laptop> <20100701115507.GA31333@redhat.com> <20100701122340.GB31333@redhat.com> <1277987657.1917.32.camel@laptop> <1277988395.1917.47.camel@laptop> <20100701130816.GB32223@redhat.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Thu, 01 Jul 2010 15:30:24 +0200 Message-ID: <1277991024.1917.108.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2110 Lines: 46 On Thu, 2010-07-01 at 16:08 +0300, Michael S. Tsirkin wrote: > On Thu, Jul 01, 2010 at 02:46:35PM +0200, Peter Zijlstra wrote: > > On Thu, 2010-07-01 at 14:34 +0200, Peter Zijlstra wrote: > > > On Thu, 2010-07-01 at 15:23 +0300, Michael S. Tsirkin wrote: > > > > > > > > The patch using this is here: > > > > http://www.mail-archive.com/kvm@vger.kernel.org/msg35411.html > > > > > > > > It simply copies the affinity from the parent when thread is created. > > > > > > Sounds like policy, not something the kernel should do.. > > > > The alternative would be using clone() instead of thread_create() and > > inherit everything from the creating task. > > Inheriting from kthreadd and then undoing some aspects just sounds > > like daft policy that really ought to be in userspace. > > Yes, that's basically what this patchset is trying to do: > create a workqueue inheriting everything from the creating task. > Sridhar started with an API to do exactly this: > http://linux.derkeiler.com/Mailing-Lists/Kernel/2010-05/msg07478.html > > Then we switched to raw kthread to avoid stepping on cwq toes. > Maybe it makes sense to add kthread_clone (in addition to > kthread_create) that would do what you suggest? > If yes, any hints on an implementation? I think that's called kernel_thread() see kernel/kthread.c:create_kthread(). Doing the whole kthreadd dance and then copying bits and pieces back sounds very fragile, so yeah, something like that should work. The other issue to consider is the thread group status of these things, I think it would be best if these threads were still considered part of the process that spawned them so that they would die nicely when the process gets whacked. At which point one could wonder if the kthread interface makes any sense, why not let userspace fork tasks and let them call into the kernel to perform work... -- 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/