Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751746Ab3HTPcB (ORCPT ); Tue, 20 Aug 2013 11:32:01 -0400 Received: from mga14.intel.com ([143.182.124.37]:47447 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751732Ab3HTPcA (ORCPT ); Tue, 20 Aug 2013 11:32:00 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.89,921,1367996400"; d="scan'208";a="349048782" Message-ID: <52138BE9.5090005@linux.intel.com> Date: Tue, 20 Aug 2013 08:31:53 -0700 From: Arjan van de Ven User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20130801 Thunderbird/17.0.8 MIME-Version: 1.0 To: Peter Zijlstra CC: =?ISO-8859-1?Q?Fernando_Luis_V=E1zquez_Cao?= , Frederic Weisbecker , Oleg Nesterov , Ingo Molnar , Thomas Gleixner , LKML , Tetsuo Handa , Andrew Morton Subject: Re: [PATCH 2/4] nohz: Synchronize sleep time stats with seqlock References: <1376667753-29014-1-git-send-email-fweisbec@gmail.com> <1376667753-29014-3-git-send-email-fweisbec@gmail.com> <20130816160201.GA31682@redhat.com> <20130816162056.GE24210@somewhere> <20130816162654.GA453@redhat.com> <20130816164626.GH24210@somewhere> <20130819111026.GE24092@twins.programming.kicks-ass.net> <521313D8.9080500@lab.ntt.co.jp> <20130820084405.GC3258@twins.programming.kicks-ass.net> In-Reply-To: <20130820084405.GC3258@twins.programming.kicks-ass.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1121 Lines: 28 On 8/20/2013 1:44 AM, Peter Zijlstra wrote: > On Tue, Aug 20, 2013 at 03:59:36PM +0900, Fernando Luis V?zquez Cao wrote: >> That said, if deemed acceptable, option A is the one I would >> choose. > > Right, so I think we can do A without much extra cost mostly because we > already have 2 atomics in the io_schedule() path. If we replace those > two atomic operations with locks and modify nr_iowait and the other > stats under the same lock, and ensure all those variables (including the > lock) live in the same cacheline we should have the same cost we have > now. > > Of course, if we can get away with completely removing all of that > (which I think Arjan suggested was a real possibility) then that would > be ever so much better still :-) I'm quite ok with removing that. however note that "top" also reports per cpu iowait... and that's a userspace expectation > -- 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/