From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755580Ab3EIXpN (ORCPT ); Thu, 9 May 2013 19:45:13 -0400 Received: from mail-wi0-f173.google.com ([209.85.212.173]:49148 "EHLO mail-wi0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755040Ab3EIXpK (ORCPT ); Thu, 9 May 2013 19:45:10 -0400 Message-ID: <518C3502.2040306@linaro.org> Date: Fri, 10 May 2013 01:45:06 +0200 From: Daniel Lezcano User-Agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130329 Thunderbird/17.0.5 MIME-Version: 1.0 To: Lianwei Wang CC: linux-kernel@vger.kernel.org, linux-pm@lists.linux-foundation.org Subject: Re: [linux-pm] [PATCH] cpuidle: don't wakeup processor when set a longer latency References: <518A324A.8000000@linaro.org> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/09/2013 09:14 AM, Lianwei Wang wrote: > Thank you very much. I have a quick updated patch based on your comments. > > diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c > index 2f0083a..cd1af4b 100644 > --- a/drivers/cpuidle/cpuidle.c > +++ b/drivers/cpuidle/cpuidle.c > @@ -18,6 +18,7 @@ > #include > #include > #include > +#include > #include > > #include "cpuidle.h" > @@ -466,7 +467,20 @@ static void smp_callback(void *v) > static int cpuidle_latency_notify(struct notifier_block *b, > unsigned long l, void *v) > { > - smp_call_function(smp_callback, NULL, 1); > + int cpu, rcpu = smp_processor_id(); > + s64 s; > + struct tick_device *td; > + > + for_each_online_cpu(cpu) { > + if (cpu == rcpu) > + continue; > + td = tick_get_device(cpu); > + s = ktime_us_delta(td->evtdev->next_event, ktime_get()); > + if ((long)l < (long)s) { > + smp_call_function_single(cpu, smp_callback, NULL, 1); > + } > + } > + > return NOTIFY_OK; > } The patch sounds reasonable. A comment and explicit names for the variables would be nice. eg. l => latency s => sleep > Thanks, > Lianwei > > 2013/5/8 Daniel Lezcano : >> On 05/08/2013 04:44 AM, Lianwei Wang wrote: >>> When a PM-Qos is updated, the cpuidle driver will wakeup all the CPUs >>> no matter what a latency is set. But actually it only need to wakeup >>> the CPUs when a shorter latency is set. In this way we can reduce the >>> cpu wakeup count and save battery. >> >> I am curious, how many times could the pm_qos be changed in a system >> live cycle to measure an improvement with this patch ? >> >> Do you have a scenario where you measured a noticeable power saving ? >> > The PM-Qos is not updated most of time, especially for home idle case. > But for some specific case, the PM-Qos may update too frequently. > (E.g. my measurement show that it is changed frequently between > 2us/3us/200us/200s for bootup and usb case.) The battery current drain > is measured from PMIC or battery eliminator. Although this is just a > little saving, it is still reasonable to improve it. Thanks for the information. Can you add this information in the changelog ? >>> So we can pass the prev_value to the notifier callback and check the >>> latency curr_value and prev_value in the cpuidle latency notifier >>> callback. It modify a common interface(dummy --> prev_value) but shall >>> be safe since no one use the dummy parameter currently. >>> >>> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c >>> index e1f6860..1e1758c 100644 >>> --- a/drivers/cpuidle/cpuidle.c >>> +++ b/drivers/cpuidle/cpuidle.c >>> @@ -498,7 +498,11 @@ static void smp_callback(void *v) >>> static int cpuidle_latency_notify(struct notifier_block *b, >>> unsigned long l, void *v) >>> { >>> - smp_call_function(smp_callback, NULL, 1); >>> + unsigned long prev_value = (unsigned long) v; >>> + >>> + /* Dont't waktup processor when set a longer latency */ >> >> ^^^^^^ >> wakeup >> >> Instead of passing prev and curr, using the dummy variable, why don't >> you pass the result of (curr - prev) ? >> >> A negative value means, the latency is smaller and positive is bigger. >> >> Also, may be the optimization could be more improved: if the latency is >> bigger than the next wakeup event, it is not necessary to wakeup the cpus. >> > This is good idea. So it need to check the next_event on each CPU and > wakeup the cpu if the requested latency is smaller than it. A quick > patch is attached. Yes, it sounds good. >>> + if (l < prev_value) >>> + smp_call_function(smp_callback, NULL, 1); >>> return NOTIFY_OK; >>> } >>> >>> diff --git a/kernel/power/qos.c b/kernel/power/qos.c >>> index 9322ff7..533b8bc 100644 >>> --- a/kernel/power/qos.c >>> +++ b/kernel/power/qos.c >>> @@ -205,7 +205,7 @@ int pm_qos_update_target(struct pm_qos_constraints >>> *c, struct plist_node *node, >>> if (prev_value != curr_value) { >>> blocking_notifier_call_chain(c->notifiers, >>> (unsigned long)curr_value, >>> - NULL); >>> + (void *)prev_value); >>> return 1; >>> } else { >>> return 0; >>> >> >> >> -- >> Linaro.org │ Open source software for ARM SoCs >> >> Follow Linaro: Facebook | >> Twitter | >> Blog >> -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog