From mboxrd@z Thu Jan 1 00:00:00 1970 From: Preeti U Murthy Subject: Re: [PATCH V2 1/5] sched: idle: cpuidle: Check the latency req before idle Date: Fri, 07 Nov 2014 09:59:24 +0530 Message-ID: <545C4AA4.7010904@linux.vnet.ibm.com> References: <1414054881-17713-1-git-send-email-daniel.lezcano@linaro.org> <544FE787.8090108@linaro.org> <54504A60.2090908@linux.vnet.ibm.com> <545A3414.7030500@linaro.org> <545AF424.2070302@linux.vnet.ibm.com> <545B7AAC.3020309@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: Received: from e32.co.us.ibm.com ([32.97.110.150]:52922 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751371AbaKGE3i (ORCPT ); Thu, 6 Nov 2014 23:29:38 -0500 Received: from /spool/local by e32.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 6 Nov 2014 21:29:37 -0700 In-Reply-To: <545B7AAC.3020309@linaro.org> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Daniel Lezcano Cc: "Rafael J. Wysocki" , Nicolas Pitre , "linux-pm@vger.kernel.org" , LKML , Peter Zijlstra , Lists linaro-kernel , patches@linaro.org On 11/06/2014 07:12 PM, Daniel Lezcano wrote: > > Preeti, > > I am wondering if we aren't going to a false debate. > > If the latency_req is 0, we should just poll and not enter in any idle > state even if one has zero exit latency. With a zero latency req, we > want full reactivity on the system, not enter an idle state with all the > computation in the menu governor, no ? > > I agree this patch changes the behavior on PowerPC, but only if the > latency_req is set to zero. I don't think we are worried about power > saving when setting this value. > > Couldn't the patch accepted as it is for the sake of consistency on all > the platform and then we optimize cleanly for the special latency zero > case ? Alright Daniel, you can go ahead. I was thinking this patch through and now realize that, like you point out the logic will only get complicated with all the additional hack. But would it be possible to add the weak arch_cpu_idle_loop() call for the cases where latency requirement is 0 like you had suggested earlier ? This would ensure the polling logic does not break on PowerPC and we don't bother the governor even. I will add the function in the core PowerPC code. If arch does not define this function it will fall back to cpu_idle_loop(). Fair enough? Regards Preeti U Murthy