Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751562AbaAOIFR (ORCPT ); Wed, 15 Jan 2014 03:05:17 -0500 Received: from e23smtp04.au.ibm.com ([202.81.31.146]:50669 "EHLO e23smtp04.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750799AbaAOIFO (ORCPT ); Wed, 15 Jan 2014 03:05:14 -0500 Message-ID: <52D6412D.8050000@linux.vnet.ibm.com> Date: Wed, 15 Jan 2014 16:05:01 +0800 From: Michael wang User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Alex Shi , mingo@redhat.com, peterz@infradead.org, tglx@linutronix.de, daniel.lezcano@linaro.org, vincent.guittot@linaro.org, morten.rasmussen@arm.com CC: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, fengguang.wu@intel.com, linaro-kernel@lists.linaro.org Subject: Re: [RFC PATCH] sched: find the latest idle cpu References: <1389758879-19951-1-git-send-email-alex.shi@linaro.org> <52D61DA0.8050206@linux.vnet.ibm.com> <52D62E96.6030301@linaro.org> In-Reply-To: <52D62E96.6030301@linaro.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14011508-9264-0000-0000-00000547DEAE Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/15/2014 02:45 PM, Alex Shi wrote: [snip] > > yes, to save your scenario, we need to know the next timer for idle cpu, > but that is not enough, interrupt is totally unpredictable. So, I'd > rather bear the coarse method now. >> >> So what about just check 'ts->tick_stopped' and record one ticking idle >> cpu? the cost could be lower than time comparison, we could reduce the >> risk may be...(well, not so risky since the logical only works when >> system is relaxing with several cpu idle) > > first, nohz full also stop tick. second, tick_stopped can not reflect > the interrupt. when the idle cpu was interrupted, it's waken, then be a > good candidate for task running. IMHO, if we have to do gamble here, we better choose the cheaper bet, unless we could prove this 'coarse method' have more higher chance for BINGO than just check 'tick_stopped'... BTW, may be the logical should be in the select_idle_sibling()? Regards, Michael Wang > -- 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/