From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934343Ab3BTHkm (ORCPT ); Wed, 20 Feb 2013 02:40:42 -0500 Received: from mout.gmx.net ([212.227.15.19]:57488 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933891Ab3BTHkl (ORCPT ); Wed, 20 Feb 2013 02:40:41 -0500 X-Authenticated: #14349625 X-Provags-ID: V01U2FsdGVkX1/to19vgpvt00GbUidH+UnpErTeNyRi8KSwAzG9F3 gsjPtRBfiL5mCD Message-ID: <1361346030.5919.63.camel@marge.simpson.net> Subject: Re: [patch v5 10/15] sched: packing transitory tasks in wake/exec power balancing From: Mike Galbraith To: Alex Shi Cc: Joonsoo Kim , torvalds@linux-foundation.org, mingo@redhat.com, peterz@infradead.org, tglx@linutronix.de, akpm@linux-foundation.org, arjan@linux.intel.com, bp@alien8.de, pjt@google.com, namhyung@kernel.org, vincent.guittot@linaro.org, gregkh@linuxfoundation.org, preeti@linux.vnet.ibm.com, viresh.kumar@linaro.org, linux-kernel@vger.kernel.org, morten.rasmussen@arm.com Date: Wed, 20 Feb 2013 08:40:30 +0100 In-Reply-To: <5124654E.8040001@intel.com> References: <1361164062-20111-1-git-send-email-alex.shi@intel.com> <1361164062-20111-11-git-send-email-alex.shi@intel.com> <20130218084439.GB10009@lge.com> <5121ECD9.3020300@intel.com> <5124654E.8040001@intel.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 X-Y-GMX-Trusted: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2013-02-20 at 13:55 +0800, Alex Shi wrote: > Joonsoo Kim suggests not packing exec task, since the old task utils is > possibly unuseable. (I'm stumbling around in rtmutex PI land, all dazed and confused, so forgive me if my peripheral following of this thread is off target;) Hm, possibly. Future behavior is always undefined, trying to predict always a gamble... so it looks to me like not packing on exec places a bet against the user, who chose to wager that powersaving will happen and it won't cost him too much, if you don't always try to pack despite any risks. The user placed a bet on powersaving, not burst performance. Same for the fork, if you spread to accommodate a potential burst, you bin the power wager, so maybe it's not in his best interest.. fork/exec is common, if it's happening frequently, you'll bin the potential power win frequently, reducing effectiveness, and silently trading power for performance when the user asked to trade performance for a lower electric bill. Dunno, just a thought, but I'd say for powersaving policy, you have to go just for broke and hope it works out. You can't know it won't, but you'll toss potential winnings every time you don't roll the dice. -Mike