Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752211AbaLQI25 (ORCPT ); Wed, 17 Dec 2014 03:28:57 -0500 Received: from mail-oi0-f43.google.com ([209.85.218.43]:32913 "EHLO mail-oi0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751692AbaLQI2z (ORCPT ); Wed, 17 Dec 2014 03:28:55 -0500 MIME-Version: 1.0 In-Reply-To: <1417529192-11579-2-git-send-email-morten.rasmussen@arm.com> References: <1417529192-11579-1-git-send-email-morten.rasmussen@arm.com> <1417529192-11579-2-git-send-email-morten.rasmussen@arm.com> From: Vincent Guittot Date: Wed, 17 Dec 2014 09:28:34 +0100 Message-ID: Subject: Re: [RFC PATCH 01/10] sched: Make load tracking frequency scale-invariant To: Morten Rasmussen Cc: Peter Zijlstra , "mingo@redhat.com" , Dietmar Eggemann , Paul Turner , Benjamin Segall , Michael Turquette , linux-kernel , "linux-pm@vger.kernel.org" Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2 December 2014 at 15:06, Morten Rasmussen wrote: > From: Dietmar Eggemann > > Apply frequency scale-invariance correction factor to load tracking. > Each segment of the sched_avg::runnable_avg_sum geometric series is now > scaled by the current frequency so the sched_avg::load_avg_contrib of each > entity will be invariant with frequency scaling. As a result, > cfs_rq::runnable_load_avg which is the sum of sched_avg::load_avg_contrib, > becomes invariant too. So the load level that is returned by > weighted_cpuload, stays relative to the max frequency of the cpu. > > Then, we want the keep the load tracking values in a 32bits type, which > implies that the max value of sched_avg::{runnable|running}_avg_sum must > be lower than 2^32/88761=48388 (88761 is the max weight of a task). As > LOAD_AVG_MAX = 47742, arch_scale_freq_capacity must return a value less > than (48388/47742) << SCHED_CAPACITY_SHIFT = 1037 (SCHED_SCALE_CAPACITY = > 1024). So we define the range to [0..SCHED_SCALE_CAPACITY] in order to > avoid overflow. > > Cc: Ingo Molnar > Cc: Peter Zijlstra > Signed-off-by: Dietmar Eggemann > --- > kernel/sched/fair.c | 28 ++++++++++++++++------------ > 1 file changed, 16 insertions(+), 12 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index ee76d52..b41f03d 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -2507,9 +2507,9 @@ static __always_inline int __update_entity_runnable_avg(u64 now, int cpu, > int runnable, > int running) > { > - u64 delta, periods; > - u32 runnable_contrib; > - int delta_w, decayed = 0; > + u64 delta, scaled_delta, periods; > + u32 runnable_contrib, scaled_runnable_contrib; > + int delta_w, scaled_delta_w, decayed = 0; > unsigned long scale_freq = arch_scale_freq_capacity(NULL, cpu); > > delta = now - sa->last_runnable_update; > @@ -2543,11 +2543,12 @@ static __always_inline int __update_entity_runnable_avg(u64 now, int cpu, > * period and accrue it. > */ > delta_w = 1024 - delta_w; > + scaled_delta_w = (delta_w * scale_freq) >> SCHED_CAPACITY_SHIFT; > + > if (runnable) > - sa->runnable_avg_sum += delta_w; > + sa->runnable_avg_sum += scaled_delta_w; > if (running) > - sa->running_avg_sum += delta_w * scale_freq > - >> SCHED_CAPACITY_SHIFT; > + sa->running_avg_sum += scaled_delta_w; > sa->avg_period += delta_w; > > delta -= delta_w; > @@ -2565,20 +2566,23 @@ static __always_inline int __update_entity_runnable_avg(u64 now, int cpu, > > /* Efficiently calculate \sum (1..n_period) 1024*y^i */ > runnable_contrib = __compute_runnable_contrib(periods); > + scaled_runnable_contrib = (runnable_contrib * scale_freq) > + >> SCHED_CAPACITY_SHIFT; > + > if (runnable) > - sa->runnable_avg_sum += runnable_contrib; > + sa->runnable_avg_sum += scaled_runnable_contrib; > if (running) > - sa->running_avg_sum += runnable_contrib * scale_freq > - >> SCHED_CAPACITY_SHIFT; > + sa->running_avg_sum += scaled_runnable_contrib; > sa->avg_period += runnable_contrib; > } > > /* Remainder of delta accrued against u_0` */ > + scaled_delta = (delta * scale_freq) >> SCHED_CAPACITY_SHIFT; > + > if (runnable) > - sa->runnable_avg_sum += delta; > + sa->runnable_avg_sum += scaled_delta; > if (running) > - sa->running_avg_sum += delta * scale_freq > - >> SCHED_CAPACITY_SHIFT; > + sa->running_avg_sum += scaled_delta; > sa->avg_period += delta; > > return decayed; Acked-by: Vincent Guittot > -- > 1.9.1 > > -- 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/