From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx113.postini.com [74.125.245.113]) by kanga.kvack.org (Postfix) with SMTP id 94E696B002C for ; Thu, 2 Feb 2012 12:07:04 -0500 (EST) Received: from /spool/local by e9.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 2 Feb 2012 12:07:01 -0500 Received: from d01relay04.pok.ibm.com (d01relay04.pok.ibm.com [9.56.227.236]) by d01dlp02.pok.ibm.com (Postfix) with ESMTP id ABDB66E8218 for ; Thu, 2 Feb 2012 12:02:57 -0500 (EST) Received: from d03av01.boulder.ibm.com (d03av01.boulder.ibm.com [9.17.195.167]) by d01relay04.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id q12H1erN033558 for ; Thu, 2 Feb 2012 12:01:40 -0500 Received: from d03av01.boulder.ibm.com (loopback [127.0.0.1]) by d03av01.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id q12H1au1015569 for ; Thu, 2 Feb 2012 10:01:39 -0700 Date: Thu, 2 Feb 2012 09:01:34 -0800 From: "Paul E. McKenney" Subject: Re: [v7 0/8] Reduce cross CPU IPI interference Message-ID: <20120202170134.GM2518@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1327572121-13673-1-git-send-email-gilad@benyossef.com> <1327591185.2446.102.camel@twins> <1328117722.2446.262.camel@twins> <20120201184045.GG2382@linux.vnet.ibm.com> <20120201201336.GI2382@linux.vnet.ibm.com> <4F2A58A1.90800@redhat.com> <20120202153437.GD2518@linux.vnet.ibm.com> <4F2AB66C.2030309@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4F2AB66C.2030309@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: Avi Kivity Cc: Christoph Lameter , Peter Zijlstra , Gilad Ben-Yossef , linux-kernel@vger.kernel.org, Chris Metcalf , Frederic Weisbecker , linux-mm@kvack.org, Pekka Enberg , Matt Mackall , Sasha Levin , Rik van Riel , Andi Kleen , Mel Gorman , Andrew Morton , Alexander Viro , Michal Nazarewicz , Kosaki Motohiro , Milton Miller On Thu, Feb 02, 2012 at 06:14:36PM +0200, Avi Kivity wrote: > On 02/02/2012 05:34 PM, Paul E. McKenney wrote: > > On Thu, Feb 02, 2012 at 11:34:25AM +0200, Avi Kivity wrote: > > > On 02/01/2012 10:13 PM, Paul E. McKenney wrote: > > > > > > > > > > Could we also apply the same approach to processors busy doing > > > > > computational work? In that case the OS is also not needed. Interrupting > > > > > these activities is impacting on performance and latency. > > > > > > > > Yep, that is in fact what Frederic's dyntick-idle userspace work does. > > > > > > Running in a guest is a special case of running in userspace, so we'd > > > need to extend this work to kvm as well. > > > > As long as rcu_idle_enter() is called at the appropriate time, RCU will > > happily ignore the CPU. ;-) > > > > It's not called (since the cpu is not idle). Instead we call > rcu_virt_note_context_switch(). Frederic's work checks to see if there is only one runnable user task on a given CPU. If there is only one, then the scheduling-clock interrupt is turned off for that CPU, and RCU is told to ignore it while it is executing in user space. Not sure whether this covers KVM guests. In any case, this is not yet in mainline. Thanx, Paul -- 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