Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932932Ab2KNLFK (ORCPT ); Wed, 14 Nov 2012 06:05:10 -0500 Received: from mail-la0-f46.google.com ([209.85.215.46]:60912 "EHLO mail-la0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932117Ab2KNLFG (ORCPT ); Wed, 14 Nov 2012 06:05:06 -0500 Message-ID: <50A37ADD.8040000@linaro.org> Date: Wed, 14 Nov 2012 12:05:01 +0100 From: Daniel Lezcano User-Agent: Mozilla/5.0 (X11; Linux i686; rv:12.0) Gecko/20120430 Thunderbird/12.0.1 MIME-Version: 1.0 To: Julius Werner CC: linux-kernel@vger.kernel.org, Len Brown , "Rafael J. Wysocki" , Kevin Hilman , Andrew Morton , "Srivatsa S. Bhat" , linux-acpi@vger.kernel.org, linux-pm@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Deepthi Dharwar , Trinabh Gupta , Sameer Nanda , Lists Linaro-dev Subject: Re: [PATCH] cpuidle: Measure idle state durations with monotonic clock References: <1352843563-16392-1-git-send-email-jwerner@chromium.org> In-Reply-To: <1352843563-16392-1-git-send-email-jwerner@chromium.org> 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 Content-Length: 4618 Lines: 119 On 11/13/2012 10:52 PM, Julius Werner wrote: > Many cpuidle drivers measure their time spent in an idle state by > reading the wallclock time before and after idling and calculating the > difference. This leads to erroneous results when the wallclock time gets > updated by another processor in the meantime, adding that clock > adjustment to the idle state's time counter. > > If the clock adjustment was negative, the result is even worse due to an > erroneous cast from int to unsigned long long of the last_residency > variable. The negative 32 bit integer will zero-extend and result in a > forward time jump of roughly four billion milliseconds or 1.3 hours on > the idle state residency counter. > > This patch changes all affected cpuidle drivers to use the monotonic > clock for their measurements instead. It also removes the erroneous > cast, making sure that negative residency values are applied correctly > even though they should not appear anymore. > > Signed-off-by: Julius Werner > --- > arch/powerpc/platforms/pseries/processor_idle.c | 4 ++-- > drivers/acpi/processor_idle.c | 12 ++++++------ > drivers/cpuidle/cpuidle.c | 3 +-- > drivers/idle/intel_idle.c | 13 ++++--------- > 4 files changed, 13 insertions(+), 19 deletions(-) > > diff --git a/arch/powerpc/platforms/pseries/processor_idle.c b/arch/powerpc/platforms/pseries/processor_idle.c > index 45d00e5..4d806b4 100644 > --- a/arch/powerpc/platforms/pseries/processor_idle.c > +++ b/arch/powerpc/platforms/pseries/processor_idle.c > @@ -36,7 +36,7 @@ static struct cpuidle_state *cpuidle_state_table; > static inline void idle_loop_prolog(unsigned long *in_purr, ktime_t *kt_before) > { > > - *kt_before = ktime_get_real(); > + *kt_before = ktime_get(); > *in_purr = mfspr(SPRN_PURR); > /* > * Indicate to the HV that we are idle. Now would be > @@ -50,7 +50,7 @@ static inline s64 idle_loop_epilog(unsigned long in_purr, ktime_t kt_before) > get_lppaca()->wait_state_cycles += mfspr(SPRN_PURR) - in_purr; > get_lppaca()->idle = 0; > > - return ktime_to_us(ktime_sub(ktime_get_real(), kt_before)); > + return ktime_to_us(ktime_sub(ktime_get(), kt_before)); > } > > static int snooze_loop(struct cpuidle_device *dev, > diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c > index e8086c7..8c98d73 100644 > --- a/drivers/acpi/processor_idle.c > +++ b/drivers/acpi/processor_idle.c > @@ -751,9 +751,9 @@ static int acpi_idle_enter_c1(struct cpuidle_device *dev, > > > lapic_timer_state_broadcast(pr, cx, 1); > - kt1 = ktime_get_real(); > + kt1 = ktime_get(); > acpi_idle_do_entry(cx); > - kt2 = ktime_get_real(); > + kt2 = ktime_get(); > idle_time = ktime_to_us(ktime_sub(kt2, kt1)); > > /* Update device last_residency*/ > @@ -843,11 +843,11 @@ static int acpi_idle_enter_simple(struct cpuidle_device *dev, > if (cx->type == ACPI_STATE_C3) > ACPI_FLUSH_CPU_CACHE(); > > - kt1 = ktime_get_real(); > + kt1 = ktime_get(); > /* Tell the scheduler that we are going deep-idle: */ > sched_clock_idle_sleep_event(); > acpi_idle_do_entry(cx); > - kt2 = ktime_get_real(); > + kt2 = ktime_get(); > idle_time_ns = ktime_to_ns(ktime_sub(kt2, kt1)); > idle_time = idle_time_ns; > do_div(idle_time, NSEC_PER_USEC); > @@ -934,7 +934,7 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev, > */ > lapic_timer_state_broadcast(pr, cx, 1); > > - kt1 = ktime_get_real(); > + kt1 = ktime_get(); > /* > * disable bus master > * bm_check implies we need ARB_DIS > @@ -965,7 +965,7 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev, > c3_cpu_count--; > raw_spin_unlock(&c3_lock); > } > - kt2 = ktime_get_real(); > + kt2 = ktime_get(); > idle_time_ns = ktime_to_ns(ktime_sub(kt2, kt1)); > idle_time = idle_time_ns; > do_div(idle_time, NSEC_PER_USEC); Maybe you can remove all these computations and set the flag en_core_tk_irqen for the driver ? That will be handled by the cpuidle framework, no ? Same comment for the intel_idle driver. Thanks -- Daniel -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog -- 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/