From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx139.postini.com [74.125.245.139]) by kanga.kvack.org (Postfix) with SMTP id C5E966B002C for ; Thu, 9 Feb 2012 10:52:56 -0500 (EST) Received: by qadz32 with SMTP id z32so4794967qad.14 for ; Thu, 09 Feb 2012 07:52:55 -0800 (PST) Date: Thu, 9 Feb 2012 16:52:49 +0100 From: Frederic Weisbecker Subject: Re: [v7 0/8] Reduce cross CPU IPI interference Message-ID: <20120209155246.GD22552@somewhere.redhat.com> References: <1327572121-13673-1-git-send-email-gilad@benyossef.com> <1327591185.2446.102.camel@twins> <20120201170443.GE6731@somewhere.redhat.com> <20120202162420.GE9071@somewhere.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Lameter Cc: Gilad Ben-Yossef , Peter Zijlstra , linux-kernel@vger.kernel.org, Chris Metcalf , linux-mm@kvack.org, Pekka Enberg , Matt Mackall , Sasha Levin , Rik van Riel , Andi Kleen , Mel Gorman , Andrew Morton , Alexander Viro , Avi Kivity , Michal Nazarewicz , Kosaki Motohiro , Milton Miller On Thu, Feb 02, 2012 at 10:29:57AM -0600, Christoph Lameter wrote: > On Thu, 2 Feb 2012, Frederic Weisbecker wrote: > > > > Some pinned timers might be able to get special treatment as well - take for > > > example the vmstat work being schedule every second, what should we do with > > > it for CPU isolation? > > > > Right, I remember I saw these vmstat timers on my way when I tried to get 0 > > interrupts on a CPU. > > > > I think all these timers need to be carefully reviewed before doing anything. > > But we certainly shouldn't adopt the behaviour of migrating timers by default. > > > > Some timers really needs to stay on the expected CPU. Note that some > > timers may be shutdown by CPU hotplug callbacks. Those wouldn't be migrated > > in case of CPU offlining. We need to keep them. > > > > > It makes sense to me to have that stop scheduling itself when we have the tick > > > disabled for both idle and a nohz task. > > The vmstat timer only makes sense when the OS is doing something on the > processor. Otherwise if no counters are incremented and the page and slab > allocator caches are empty then there is no need to run the vmstat timer. So this is a typical example of a timer we want to shutdown when the CPU is idle but we want to keep it running when we run in adaptive tickless mode (ie: shutdown the tick while the CPU is busy). -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org