Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751149AbaKZI2M (ORCPT ); Wed, 26 Nov 2014 03:28:12 -0500 Received: from mail-oi0-f53.google.com ([209.85.218.53]:58963 "EHLO mail-oi0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750954AbaKZI2L (ORCPT ); Wed, 26 Nov 2014 03:28:11 -0500 MIME-Version: 1.0 In-Reply-To: <5475628D.2080301@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> <5475628D.2080301@gmail.com> From: Vincent Guittot Date: Wed, 26 Nov 2014 09:27:50 +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 26 November 2014 at 06:18, Wanpeng Li wrote: > Hi Vincent, > > On 11/25/14, 9:52 PM, Vincent Guittot wrote: >> >> 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 >> . > > > Do you mean 'sched_avg_period() + delta' should be replaced by 'delta' since > sched_avg_period() is "long"? No, Both are useful. sched_avg_period is useful to keep the value more stable across the time. Without sched_avg_period, it will be too much reactive ( especially at the beg of a period ). > > Regards, > Wanpeng Li > > >> >>> 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 >>> >>> > -- 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/