From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755115Ab0CHS2w (ORCPT ); Mon, 8 Mar 2010 13:28:52 -0500 Received: from mx1.redhat.com ([209.132.183.28]:15028 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752331Ab0CHS2r (ORCPT ); Mon, 8 Mar 2010 13:28:47 -0500 Date: Mon, 8 Mar 2010 19:27:08 +0100 From: Oleg Nesterov To: Heiko Carstens Cc: Tejun Heo , linux-kernel@vger.kernel.org, rusty@rustcorp.com.au, sivanich@sgi.com, torvalds@linux-foundation.org, mingo@elte.hu, peterz@infradead.org, dipankar@in.ibm.com, josh@freedesktop.org, paulmck@linux.vnet.ibm.com, akpm@linux-foundation.org, Martin Schwidefsky Subject: Re: [PATCH 2/4] stop_machine: reimplement using cpuhog Message-ID: <20100308182708.GA8504@redhat.com> References: <1268063603-7425-1-git-send-email-tj@kernel.org> <1268063603-7425-3-git-send-email-tj@kernel.org> <20100308171020.GC2557@osiris.boeblingen.de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100308171020.GC2557@osiris.boeblingen.de.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/08, Heiko Carstens wrote: > > On Tue, Mar 09, 2010 at 12:53:21AM +0900, Tejun Heo wrote: > > > > diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c > > index 65065ac..afe429e 100644 > > --- a/arch/s390/kernel/time.c > > +++ b/arch/s390/kernel/time.c > > @@ -397,7 +397,6 @@ static void __init time_init_wq(void) > > if (time_sync_wq) > > return; > > time_sync_wq = create_singlethread_workqueue("timesync"); > > - stop_machine_create(); > > } > > > > /* > > The reason we introduced stop_machine_create/destroy was to have a non-failing > variant that doesn't rely on I/O. > If we ever see a timesync machine check no I/O will succeed (it blocks) until > clocks have been synchronized. That means also that we rely on the non-blocking > semantics that those functions must have that are called via stop_machine. > This isn't true anymore with the cpu hog infrastructure: > if passed a blocking function that could wait on I/O we won't see any progress > anymore and the machine is dead. Could you please spell? How cpuhog can make a difference? Afaics, we shouldn't pass a blocking callback to hog_cpus/hog_one_cpu. Oleg.