Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754921Ab2KBOuq (ORCPT ); Fri, 2 Nov 2012 10:50:46 -0400 Received: from mail-bk0-f46.google.com ([209.85.214.46]:38500 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750954Ab2KBOup (ORCPT ); Fri, 2 Nov 2012 10:50:45 -0400 Message-ID: <5093DDBD.4000603@gmail.com> Date: Fri, 02 Nov 2012 15:50:37 +0100 From: =?ISO-8859-15?Q?David_Nystr=F6m?= User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121028 Thunderbird/16.0.2 MIME-Version: 1.0 To: Steven Rostedt CC: Christoph Lameter , linux-kernel@vger.kernel.org, Andrew Morton , Thomas Gleixner , Peter Zijlstra , Clark Williams , Frederic Weisbecker , Li Zefan , Ingo Molnar , "Paul E. McKenney" , Mike Galbraith Subject: Re: [PATCH 00/32] [RFC] nohz/cpuset: Start discussions on nohz CPUs References: <20121029202711.062749374@goodmis.org> <0000013ac180f152-79f05c71-4d38-43b0-9b62-8a71c00dfda7-000000@email.amazonses.com> <1351867045.4004.141.camel@gandalf.local.home> In-Reply-To: <1351867045.4004.141.camel@gandalf.local.home> Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1578 Lines: 43 On 11/02/2012 03:37 PM, Steven Rostedt wrote: > On Fri, 2012-11-02 at 14:23 +0000, Christoph Lameter wrote: >> On Mon, 29 Oct 2012, Steven Rostedt wrote: >> >>> A while ago Frederic posted a series of patches to get an idea on >>> how to implement nohz cpusets. Where you can add a task to a cpuset >>> and mark the set to be 'nohz'. When the task runs on a CPU and is >>> the only task scheduled (nr_running == 1), the tick will stop. >>> The idea is to give the task the least amount of kernel interference >>> as possible. If the task doesn't do any system calls (and possibly >>> even if it does), no timer interrupt will bother it. By using >>> isocpus and nohz cpuset, a task would be able to achieve true cpu >>> isolation. >> One other aspect that this patch probably needs to address is the cache localization of irq spinlocks. At least in 3.6, with !CONFIG_SPARSE_IRQ -- struct irq_desc irq_desc[NR_IRQS] __cacheline_aligned_in_smp = { [0 ... NR_IRQS-1] = { .handle_irq = handle_bad_irq, .depth = 1, .lock = __RAW_SPIN_LOCK_UNLOCKED(irq_desc->lock), } }; -- You are likely to get a cache miss in the top half of your low latency CPU anytime some other CPU has taken a spinlock which lies within the same cache line. Or is my understanding of the __cacheline_aligned_in_smp declaration wrong ? Br, David -- 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/