From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2A54EC00528 for ; Mon, 24 Jul 2023 15:33:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231361AbjGXPdv (ORCPT ); Mon, 24 Jul 2023 11:33:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51146 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229544AbjGXPdt (ORCPT ); Mon, 24 Jul 2023 11:33:49 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id A0170B1; Mon, 24 Jul 2023 08:33:47 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 7A35DFEC; Mon, 24 Jul 2023 08:34:30 -0700 (PDT) Received: from [10.34.100.101] (e126645.nice.arm.com [10.34.100.101]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 04D383F67D; Mon, 24 Jul 2023 08:33:44 -0700 (PDT) Message-ID: <18b0d54b-f8d2-ff38-f5c8-697dc838e3ce@arm.com> Date: Mon, 24 Jul 2023 17:33:34 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH] cpufreq: schedutil: next_freq need update when cpufreq_limits changed Content-Language: en-US To: Xuewen Yan , Qais Yousef Cc: Xuewen Yan , rafael@kernel.org, viresh.kumar@linaro.org, mingo@redhat.com, peterz@infradead.org, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, guohua.yan@unisoc.com, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20230719130527.8074-1-xuewen.yan@unisoc.com> <20230721221944.dthg3tf25j4qgc2z@airbuntu> From: Pierre Gondois In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/24/23 05:36, Xuewen Yan wrote: > On Sat, Jul 22, 2023 at 7:02 AM Qais Yousef wrote: >> >> On 07/19/23 21:05, Xuewen Yan wrote: >>> When cpufreq's policy is single, there is a scenario that will >>> cause sg_policy's next_freq to be unable to update. >>> >>> When the cpu's util is always max, the cpufreq will be max, >>> and then if we change the policy's scaling_max_freq to be a >>> lower freq, indeed, the sg_policy's next_freq need change to >>> be the lower freq, however, because the cpu_is_busy, the next_freq >>> would keep the max_freq. >>> >>> For example: >>> The cpu7 is single cpu: >>> >>> unisoc:/sys/devices/system/cpu/cpufreq/policy7 # while true;do done& >>> [1] 4737 >>> unisoc:/sys/devices/system/cpu/cpufreq/policy7 # taskset -p 80 4737 >>> pid 4737's current affinity mask: ff >>> pid 4737's new affinity mask: 80 >>> unisoc:/sys/devices/system/cpu/cpufreq/policy7 # cat scaling_max_freq >>> 2301000 >>> unisoc:/sys/devices/system/cpu/cpufreq/policy7 # cat scaling_cur_freq >>> 2301000 >>> unisoc:/sys/devices/system/cpu/cpufreq/policy7 # echo 2171000 > scaling_max_freq >>> unisoc:/sys/devices/system/cpu/cpufreq/policy7 # cat scaling_max_freq >>> 2171000 >>> >>> At this time, the sg_policy's next_freq would keep 2301000. >>> >>> To prevent the case happen, add the judgment of the need_freq_update flag. >>> >>> Signed-off-by: Xuewen Yan >>> Co-developed-by: Guohua Yan >>> Signed-off-by: Guohua Yan >>> --- >>> kernel/sched/cpufreq_schedutil.c | 3 ++- >>> 1 file changed, 2 insertions(+), 1 deletion(-) >>> >>> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c >>> index 4492608b7d7f..458d359f5991 100644 >>> --- a/kernel/sched/cpufreq_schedutil.c >>> +++ b/kernel/sched/cpufreq_schedutil.c >>> @@ -350,7 +350,8 @@ static void sugov_update_single_freq(struct update_util_data *hook, u64 time, >>> * Except when the rq is capped by uclamp_max. >>> */ >>> if (!uclamp_rq_is_capped(cpu_rq(sg_cpu->cpu)) && >>> - sugov_cpu_is_busy(sg_cpu) && next_f < sg_policy->next_freq) { >>> + sugov_cpu_is_busy(sg_cpu) && next_f < sg_policy->next_freq && >>> + !sg_policy->need_freq_update) { >> >> What about sugov_update_single_perf()? It seems to have the same problem, no? > > There is no problem in sugov_update_single_perf, because the next_freq > is updated by drivers, maybe the next_freq is not used when using > sugov_update_single_perf.. > > But for the last_freq_update_time, I think there are some problems > when using sugov_update_single_perf: > Now, there is no judgment condition for the update of the > last_freq_update_time. That means the last_freq_update_time is always > updated in sugov_update_single_perf. > And in sugov_should_update_freq: it would judge the > freq_update_delay_ns. As a result, If we use the > sugov_update_single_perf, the cpu frequency would only be periodically > updated according to freq_update_delay_ns. > Maybe we should judge the cpufreq_driver_adjust_perf's return value, > if the freq is not updated, the last_freq_update_time also does not > have to update. > > Just like: > --- > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c > index 458d359f5991..10f18b054f01 100644 > --- a/kernel/sched/cpufreq_schedutil.c > +++ b/kernel/sched/cpufreq_schedutil.c > @@ -381,6 +381,7 @@ static void sugov_update_single_perf(struct > update_util_data *hook, u64 time, > struct sugov_cpu *sg_cpu = container_of(hook, struct > sugov_cpu, update_util); > unsigned long prev_util = sg_cpu->util; > unsigned long max_cap; > + bool freq_updated; > > /* > * Fall back to the "frequency" path if frequency invariance is not > @@ -407,10 +408,11 @@ static void sugov_update_single_perf(struct > update_util_data *hook, u64 time, > sugov_cpu_is_busy(sg_cpu) && sg_cpu->util < prev_util) > sg_cpu->util = prev_util; > > - cpufreq_driver_adjust_perf(sg_cpu->cpu, map_util_perf(sg_cpu->bw_dl), > + freq_updated = cpufreq_driver_adjust_perf(sg_cpu->cpu, > map_util_perf(sg_cpu->bw_dl), > map_util_perf(sg_cpu->util), max_cap); > > - sg_cpu->sg_policy->last_freq_update_time = time; > + if (freq_updated) > + sg_cpu->sg_policy->last_freq_update_time = time; > } > Hello Xuewen, FWIW, the patch and explanation for sugov_update_single_perf() seem sensible to me. Just a comment about cpufreq_driver_adjust_perf() and (struct cpufreq_driver)->adjust_perf(): wouldn't their prototype need to be updated (i.e. not return void) to do the change suggested above ? Regards, Pierre > > BR > Thanks! > > --- > xuewen >> >> LGTM otherwise. >> >> >> Cheers >> >> -- >> Qais Yousef >> >>> next_f = sg_policy->next_freq; >>> >>> /* Restore cached freq as next_freq has changed */ >>> -- >>> 2.25.1 >>> >