From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753945Ab0CHRKR (ORCPT ); Mon, 8 Mar 2010 12:10:17 -0500 Received: from mtagate4.uk.ibm.com ([194.196.100.164]:36807 "EHLO mtagate4.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751656Ab0CHRKL (ORCPT ); Mon, 8 Mar 2010 12:10:11 -0500 Date: Mon, 8 Mar 2010 18:10:20 +0100 From: Heiko Carstens To: Tejun Heo Cc: 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, oleg@redhat.com, akpm@linux-foundation.org, Martin Schwidefsky Subject: Re: [PATCH 2/4] stop_machine: reimplement using cpuhog Message-ID: <20100308171020.GC2557@osiris.boeblingen.de.ibm.com> References: <1268063603-7425-1-git-send-email-tj@kernel.org> <1268063603-7425-3-git-send-email-tj@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1268063603-7425-3-git-send-email-tj@kernel.org> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 09, 2010 at 12:53:21AM +0900, Tejun Heo wrote: > Reimplement stop_machine using cpuhog. As cpuhogs are guaranteed to > be available for all online cpus, stop_machine_create/destroy() are no > longer necessary and removed. > > With resource management and synchronization handled by cpuhog, the > new implementation is much simpler. Asking the cpuhog to execute the > stop_cpu() state machine on all online cpus with cpu hotplug disabled > is enough. > > stop_machine itself doesn't need to manage any global resources > anymore, so all per-instance information is rolled into struct > stop_machine_data and the mutex and all static data variables are > removed. > > The previous implementation created and destroyed RT workqueues as > necessary which made stop_machine() calls highly expensive on very > large machines. According to Dimitri Sivanich, preventing the dynamic > creation/destruction makes booting faster more than twice on very > large machines. cpuhog resources are preallocated for all online cpus > and should have the same effect. > > Signed-off-by: Tejun Heo > Cc: Rusty Russell > Cc: Oleg Nesterov > Cc: Dimitri Sivanich > --- > arch/s390/kernel/time.c | 1 - > drivers/xen/manage.c | 14 +--- > include/linux/stop_machine.h | 20 ----- > kernel/cpu.c | 8 -- > kernel/module.c | 14 +--- > kernel/stop_machine.c | 162 ++++++++++-------------------------------- > 6 files changed, 42 insertions(+), 177 deletions(-) > > 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.