Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757060Ab3GECsH (ORCPT ); Thu, 4 Jul 2013 22:48:07 -0400 Received: from e28smtp08.in.ibm.com ([122.248.162.8]:33849 "EHLO e28smtp08.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755500Ab3GECsF (ORCPT ); Thu, 4 Jul 2013 22:48:05 -0400 Message-ID: <51D633DB.5010508@linux.vnet.ibm.com> Date: Fri, 05 Jul 2013 10:47:55 +0800 From: Michael Wang User-Agent: Mozilla/5.0 (X11; Linux i686; rv:16.0) Gecko/20121011 Thunderbird/16.0.1 MIME-Version: 1.0 To: Mike Galbraith CC: Peter Zijlstra , LKML , Ingo Molnar , Alex Shi , Namhyung Kim , Paul Turner , Andrew Morton , "Nikunj A. Dadhania" , Ram Pai Subject: Re: [PATCH] sched: smart wake-affine References: <51A43B16.9080801@linux.vnet.ibm.com> <51D25A80.8090406@linux.vnet.ibm.com> <20130702085202.GA23916@twins.programming.kicks-ass.net> <51D29EE5.8080307@linux.vnet.ibm.com> <20130704091339.GK18898@dyad.programming.kicks-ass.net> <51D5428D.7080805@linux.vnet.ibm.com> <1372934013.9046.16.camel@marge.simpson.net> In-Reply-To: <1372934013.9046.16.camel@marge.simpson.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13070502-2000-0000-0000-00000CC399AC Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3145 Lines: 80 On 07/04/2013 06:33 PM, Mike Galbraith wrote: [snip] >> Well, seems like we still have many follow-up research works after fix >> the issue ;-) > > Yeah. Like how to how to exterminate the plus sign, they munch cache > lines, and have a general tendency to negatively impact benchmarks. > > Q6600 box, hackbench -l 1000 > avg > 3.10.0-regress 2.293 2.297 2.313 2.291 2.295 2.297 1.000 > 3.10.0-regressx 2.560 2.524 2.427 2.599 2.602 2.542 1.106 Wow, I used to think such issue is very hard to be tracked by benchmarks, is this regression stable? My test could not get a stable differ, this time a little bit lose but next time a little bit win, it's always floating, may caused by the different chip cache-behaviour I suppose... > > pahole said... > > marge:/usr/local/src/kernel/linux-3.x.git # tail virgin > long unsigned int timer_slack_ns; /* 1512 8 */ > long unsigned int default_timer_slack_ns; /* 1520 8 */ > atomic_t ptrace_bp_refcnt; /* 1528 4 */ > > /* size: 1536, cachelines: 24, members: 125 */ > /* sum members: 1509, holes: 6, sum holes: 23 */ > /* bit holes: 1, sum bit holes: 26 bits */ > /* padding: 4 */ > /* paddings: 1, sum paddings: 4 */ > }; > > marge:/usr/local/src/kernel/linux-3.x.git # tail michael > long unsigned int default_timer_slack_ns; /* 1552 8 */ > atomic_t ptrace_bp_refcnt; /* 1560 4 */ > > /* size: 1568, cachelines: 25, members: 128 */ > /* sum members: 1533, holes: 8, sum holes: 31 */ > /* bit holes: 1, sum bit holes: 26 bits */ > /* padding: 4 */ > /* paddings: 1, sum paddings: 4 */ > /* last cacheline: 32 bytes */ > }; > > ..but plugging holes, didn't help, moving this/that around neither, nor > did letting pahole go wild to get the line back. It's plus signs I tell > ya, the evil things must die ;-) Hmm...so the new members kicked some tail members to a new line...or may be totally different when compiler take part in... It's really hard to estimate the influence, especially when the task_struct is still keep changing... But the task_struct is really a little big now, may be we could put the 'cold' members into a new structure and just record the pointer, that may increase the chances of cache-hit the hot members, but it's platform related and not so easy to be detect... Regards, Michael Wang > > -Mike > > -- > 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/ > -- 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/