From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751658AbaKYCYw (ORCPT ); Mon, 24 Nov 2014 21:24:52 -0500 Received: from mail-pd0-f173.google.com ([209.85.192.173]:40870 "EHLO mail-pd0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750830AbaKYCYv (ORCPT ); Mon, 24 Nov 2014 21:24:51 -0500 Message-ID: <5473E867.6030607@gmail.com> Date: Tue, 25 Nov 2014 10:24:39 +0800 From: Wanpeng Li User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Vincent Guittot , peterz@infradead.org, mingo@kernel.org, linux-kernel@vger.kernel.org, preeti@linux.vnet.ibm.com, Morten.Rasmussen@arm.com, kamalesh@linux.vnet.ibm.com, linux-arm-kernel@lists.infradead.org CC: riel@redhat.com, efault@gmx.de, nicolas.pitre@linaro.org, linaro-kernel@lists.linaro.org Subject: Re: [PATCH v9 05/10] sched: make scale_rt invariant with frequency References: <1415033687-23294-1-git-send-email-vincent.guittot@linaro.org> <1415033687-23294-6-git-send-email-vincent.guittot@linaro.org> In-Reply-To: <1415033687-23294-6-git-send-email-vincent.guittot@linaro.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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()? 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