Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754994Ab3CLGAm (ORCPT ); Tue, 12 Mar 2013 02:00:42 -0400 Received: from e23smtp03.au.ibm.com ([202.81.31.145]:38781 "EHLO e23smtp03.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754315Ab3CLGAl (ORCPT ); Tue, 12 Mar 2013 02:00:41 -0400 Message-ID: <513EC47E.9040602@linux.vnet.ibm.com> Date: Tue, 12 Mar 2013 14:00:30 +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: Ingo Molnar CC: Peter Zijlstra , LKML , Mike Galbraith , Namhyung Kim , Alex Shi , Paul Turner , Andrew Morton , "Nikunj A. Dadhania" , Ram Pai Subject: Re: [PATCH] sched: wakeup buddy References: <5136EB06.2050905@linux.vnet.ibm.com> <1362645372.2606.11.camel@laptop> <20130311082105.GB12742@gmail.com> <513DA076.80009@linux.vnet.ibm.com> <20130311094031.GA14221@gmail.com> In-Reply-To: <20130311094031.GA14221@gmail.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13031205-6102-0000-0000-00000323D06F Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2587 Lines: 71 On 03/11/2013 05:40 PM, Ingo Molnar wrote: > > * Michael Wang wrote: > >> Hi, Ingo >> >> On 03/11/2013 04:21 PM, Ingo Molnar wrote: >> [snip] >>> >>> I have actually written the prctl() approach before, for instrumentation >>> purposes, and it does wonders to system analysis. >> >> The idea sounds great, we could get many new info to implement more >> smart scheduler, that's amazing :) >> >>> >>> Any objections? >> >> Just one concern, may be I have misunderstand you, but will it cause >> trouble if the prctl() was indiscriminately used by some applications, >> will we get fake data? > > It's their problem: overusing it will increase their CPU overhead. The two > boundary worst-cases are that they either call it too frequently or too > rarely: > > - too frequently: it approximates the current cpu-runtime work metric > > - too infrequently: we just ignore it and fall back to a runtime metric > if it does not change. > > It's not like it can be used to get preferential treatment - we don't ever > balance other tasks against these tasks based on work throughput, we try > to maximize this workload's work throughput. > > What could happen is if an app is 'optimized' for a buggy scheduler by > changing the work metric frequency. We offer no guarantee - apps will be > best off (and users will be least annoyed) if apps honestly report their > work metric. > > Instrumentation/stats/profiling will also double check the correctness of > this data: if developers/users start relying on the work metric as a > substitute benchmark number, then app writers will have an additional > incentive to make them correct. I see, I could not figure out how to wisely using the info currently, but I have the feeling that it will make scheduler very different ;-) May be we could implement the API and get those info ready firstly (along with the new sched-pipe which provide work tick info), then think about the way to use them in scheduler, is there any patches on the way? Regards, Michael Wang > > Thanks, > > Ingo > -- > 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/