Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S269430AbUIILQh (ORCPT ); Thu, 9 Sep 2004 07:16:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S269433AbUIILQf (ORCPT ); Thu, 9 Sep 2004 07:16:35 -0400 Received: from smtp209.mail.sc5.yahoo.com ([216.136.130.117]:64182 "HELO smtp209.mail.sc5.yahoo.com") by vger.kernel.org with SMTP id S269436AbUIILQR (ORCPT ); Thu, 9 Sep 2004 07:16:17 -0400 Message-ID: <414037B0.40803@yahoo.com.au> Date: Thu, 09 Sep 2004 21:00:00 +1000 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.2) Gecko/20040810 Debian/1.7.2-2 X-Accept-Language: en MIME-Version: 1.0 To: Rusty Russell CC: Nathan Lynch , linux-kernel Subject: Re: [PATCH 2/3] cpu: add a CPU_DOWN_PREPARE notifier References: <413EFFFB.5050902@yahoo.com.au> <413F0070.2020104@yahoo.com.au> <1094725418.25641.21.camel@bach> <41402F73.6060804@yahoo.com.au> In-Reply-To: <41402F73.6060804@yahoo.com.au> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1727 Lines: 46 Nick Piggin wrote: > Rusty Russell wrote: > >> On Wed, 2004-09-08 at 22:52, Nick Piggin wrote: >> >>> 2/3 >>> >>> Rusty, can I do this? >>> >>> ______________________________________________________________________ >>> Add a CPU_DOWN_PREPARE hotplug CPU notifier. This is needed so we can >>> dettach all sched-domains before a CPU goes down, thus we can build >>> domains from online cpumasks, and not have to check for the possibility >>> of a CPU coming up or going down. >> >> >> >> And if taking the CPU down fails? If you need this, you need the >> CPU_DOWN_FAILED as well, unfortunately. Hence I prefer the "do the >> domain thing while machine is frozen" and sidestep it entirely. >> > > Really? It doesn't need to be run from the stop_machine_run > context at all - it can happily be done while the system is > running. > > That said, if you really object to CPU_DOWN_PREPARE and CPU_DOWN_FAILED, > it probably shouldn't be too much work. Should it make the call from > take_cpu_down? > The other thing is, it is actually a lot nicer to have this done while the machine is running, because then cpu_attach_domain guarantees a quiescent state, so the attach can be done completely atomically from the point of view of the rest of the scheduler. So you can always rely on domains and cpu_online_map staying in synch. The alternative is more fastpath checking of the cpu_online_map, and possibly more hotplug locks. In short, I'd really like to have it done this way. - 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/