From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754923Ab3EHLJB (ORCPT ); Wed, 8 May 2013 07:09:01 -0400 Received: from mail-ee0-f41.google.com ([74.125.83.41]:58099 "EHLO mail-ee0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754732Ab3EHLJA (ORCPT ); Wed, 8 May 2013 07:09:00 -0400 Message-ID: <518A324A.8000000@linaro.org> Date: Wed, 08 May 2013 13:08:58 +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: 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 05/08/2013 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 ? > 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. > + 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