From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751211AbaKYNwq (ORCPT ); Tue, 25 Nov 2014 08:52:46 -0500 Received: from mail-oi0-f51.google.com ([209.85.218.51]:46601 "EHLO mail-oi0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750918AbaKYNwp (ORCPT ); Tue, 25 Nov 2014 08:52:45 -0500 MIME-Version: 1.0 In-Reply-To: <5473E867.6030607@gmail.com> References: <1415033687-23294-1-git-send-email-vincent.guittot@linaro.org> <1415033687-23294-6-git-send-email-vincent.guittot@linaro.org> <5473E867.6030607@gmail.com> From: Vincent Guittot Date: Tue, 25 Nov 2014 14:52:24 +0100 Message-ID: Subject: Re: [PATCH v9 05/10] sched: make scale_rt invariant with frequency To: Wanpeng Li Cc: Peter Zijlstra , Ingo Molnar , linux-kernel , Preeti U Murthy , Morten Rasmussen , Kamalesh Babulal , LAK , Rik van Riel , Mike Galbraith , Nicolas Pitre , "linaro-kernel@lists.linaro.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 25 November 2014 at 03:24, Wanpeng Li wrote: > Hi Vincent, > On 11/4/14, 12:54 AM, Vincent Guittot wrote: >> >> The average running time of RT tasks is used to estimate the remaining >> compute >> capacity for CFS tasks. This remaining capacity is the original capacity >> scaled >> down by a factor (aka scale_rt_capacity). This estimation of available >> capacity >> must also be invariant with frequency scaling. >> >> A frequency scaling factor is applied on the running time of the RT tasks >> for >> computing scale_rt_capacity. >> >> In sched_rt_avg_update, we scale the RT execution time like below: >> rq->rt_avg += rt_delta * arch_scale_freq_capacity() >> >> SCHED_CAPACITY_SHIFT >> >> Then, scale_rt_capacity can be summarized by: >> scale_rt_capacity = SCHED_CAPACITY_SCALE - >> ((rq->rt_avg << SCHED_CAPACITY_SHIFT) / period) > > > The 'period' aka 'total' in the scale_rt_capacity(), why it is > sched_avg_period() + delta instead of sched_avg_period()? The default value of sched_avg_period is 1sec which is "long" so we take into account the time consumed by RT tasks in the ongoing period . > > Regards, > Wanpeng Li > > >> >> We can optimize by removing right and left shift in the computation of >> rq->rt_avg >> and scale_rt_capacity >> >> The call to arch_scale_frequency_capacity in the rt scheduling path might >> be >> a concern for RT folks because I'm not sure whether we can rely on >> arch_scale_freq_capacity to be short and efficient ? >> >> Signed-off-by: Vincent Guittot >> --- >> kernel/sched/fair.c | 17 +++++------------ >> kernel/sched/sched.h | 4 +++- >> 2 files changed, 8 insertions(+), 13 deletions(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index a5039da..b37c27b 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -5785,7 +5785,7 @@ unsigned long __weak arch_scale_cpu_capacity(struct >> sched_domain *sd, int cpu) >> static unsigned long scale_rt_capacity(int cpu) >> { >> struct rq *rq = cpu_rq(cpu); >> - u64 total, available, age_stamp, avg; >> + u64 total, used, age_stamp, avg; >> s64 delta; >> /* >> @@ -5801,19 +5801,12 @@ static unsigned long scale_rt_capacity(int cpu) >> total = sched_avg_period() + delta; >> - if (unlikely(total < avg)) { >> - /* Ensures that capacity won't end up being negative */ >> - available = 0; >> - } else { >> - available = total - avg; >> - } >> + used = div_u64(avg, total); >> - if (unlikely((s64)total < SCHED_CAPACITY_SCALE)) >> - total = SCHED_CAPACITY_SCALE; >> + if (likely(used < SCHED_CAPACITY_SCALE)) >> + return SCHED_CAPACITY_SCALE - used; >> - total >>= SCHED_CAPACITY_SHIFT; >> - >> - return div_u64(available, total); >> + return 1; >> } >> static void update_cpu_capacity(struct sched_domain *sd, int cpu) >> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h >> index c34bd11..fc5b152 100644 >> --- a/kernel/sched/sched.h >> +++ b/kernel/sched/sched.h >> @@ -1312,9 +1312,11 @@ static inline int hrtick_enabled(struct rq *rq) >> #ifdef CONFIG_SMP >> extern void sched_avg_update(struct rq *rq); >> +extern unsigned long arch_scale_freq_capacity(struct sched_domain *sd, >> int cpu); >> + >> static inline void sched_rt_avg_update(struct rq *rq, u64 rt_delta) >> { >> - rq->rt_avg += rt_delta; >> + rq->rt_avg += rt_delta * arch_scale_freq_capacity(NULL, >> cpu_of(rq)); >> sched_avg_update(rq); >> } >> #else > >