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[2620:137:e000::1:20]) by mx.google.com with ESMTP id n22-20020a63ee56000000b003983fed820asi1324606pgk.242.2022.04.11.17.54.12; Mon, 11 Apr 2022 17:54:27 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=arm.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243386AbiDKOJo (ORCPT + 99 others); Mon, 11 Apr 2022 10:09:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57356 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346838AbiDKOJm (ORCPT ); Mon, 11 Apr 2022 10:09:42 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 8FE34329B8 for ; Mon, 11 Apr 2022 07:07:28 -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 48E2B1570; Mon, 11 Apr 2022 07:07:28 -0700 (PDT) Received: from [192.168.178.6] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 4C6763F73B; Mon, 11 Apr 2022 07:07:26 -0700 (PDT) Message-ID: <9bb00bcb-f984-1cf6-39aa-c11dcf7f07cb@arm.com> Date: Mon, 11 Apr 2022 16:07:14 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [PATCH] sched: Take thermal pressure into account when determine rt fits capacity Content-Language: en-US To: Xuewen Yan Cc: Xuewen Yan , Lukasz.Luba@arm.com, rafael@kernel.org, viresh.kumar@linaro.org, mingo@redhat.com, peterz@infradead.org, vincent.guittot@linaro.org, rostedt@goodmis.org, linux-kernel@vger.kernel.org, di.shen@unisoc.com References: <20220407051932.4071-1-xuewen.yan@unisoc.com> <02350916-aa36-ea53-2c98-91b97f49d27e@arm.com> From: Dietmar Eggemann In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-8.5 required=5.0 tests=BAYES_00,NICE_REPLY_A, RCVD_IN_DNSWL_HI,SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/04/2022 10:52, Xuewen Yan wrote: > HI Dietmar > > On Mon, Apr 11, 2022 at 4:21 PM Dietmar Eggemann > wrote: >> >> On 07/04/2022 07:19, Xuewen Yan wrote: >>> There are cases when the cpu max capacity might be reduced due to thermal. >>> Take into the thermal pressure into account when judge whether the rt task >>> fits the cpu. And when schedutil govnor get cpu util, the thermal pressure >>> also should be considered. >>> >>> Signed-off-by: Xuewen Yan >>> --- >>> kernel/sched/cpufreq_schedutil.c | 1 + >>> kernel/sched/rt.c | 1 + >>> 2 files changed, 2 insertions(+) >>> >>> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c >>> index 3dbf351d12d5..285ad51caf0f 100644 >>> --- a/kernel/sched/cpufreq_schedutil.c >>> +++ b/kernel/sched/cpufreq_schedutil.c >>> @@ -159,6 +159,7 @@ static void sugov_get_util(struct sugov_cpu *sg_cpu) >>> struct rq *rq = cpu_rq(sg_cpu->cpu); >>> unsigned long max = arch_scale_cpu_capacity(sg_cpu->cpu); >>> >>> + max -= arch_scale_thermal_pressure(sg_cpu->cpu); >> >> max' = arch_scale_cpu_capacity() - arch_scale_thermal_pressure() >> >> For the energy part (A) we use max' in compute_energy() to cap sum_util >> and max_util at max' and to call em_cpu_energy(..., max_util, sum_util, >> max'). This was done to match (B)'s `policy->max` capping. >> >> For the frequency part (B) we have freq_qos_update_request() in: >> >> power_actor_set_power() >> ... >> cdev->ops->set_cur_state() >> >> cpufreq_set_cur_state() >> freq_qos_update_request() <-- ! >> arch_update_thermal_pressure() >> >> restricting `policy->max` which then clamps `target_freq` in: >> >> cpufreq_update_util() >> ... >> get_next_freq() >> cpufreq_driver_resolve_freq() >> __resolve_freq() >> > > Do you mean that the "max" here will not affect the frequency > conversion, so there is no need to change it? > But is it better to reflect the influence of thermal here? I guess your point is that even though max' has no effect on frequency since QOS caps policy->max anyway, it is still easier to understand the dependency between schedutil and EAS/EM when it comes to the use of thermal pressure. I agree. The way how the "hidden" policy->max capping guarantees that schedutil and EAS/EM are doing the same even when only the latter uses max' is not obvious. I just wanted to mention the historical reason why the code looks like it does today. >> [...] >> >>> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c >>> index a32c46889af8..d9982ebd4821 100644 >>> --- a/kernel/sched/rt.c >>> +++ b/kernel/sched/rt.c >>> @@ -466,6 +466,7 @@ static inline bool rt_task_fits_capacity(struct task_struct *p, int cpu) >>> max_cap = uclamp_eff_value(p, UCLAMP_MAX); >>> >>> cpu_cap = capacity_orig_of(cpu); >>> + cpu_cap -= arch_scale_thermal_pressure(cpu); >>> >>> return cpu_cap >= min(min_cap, max_cap); >>> } >> >> IMHO, this should follow what we do with rq->cpu_capacity >> (capacity_of(), the remaining capacity for CFS). E.g. we use >> capacity_of() in find_energy_efficient_cpu() and select_idle_capacity() >> to compare capacities. So we would need a function like >> scale_rt_capacity() for RT (minus the rq->avg_rt.util_avg) but then also >> one for DL (minus rq->avg_dl.util_avg and rq->avg_rt.util_avg). > > It's a really good idea. And do you already have the corresponding patch? > If there is, can you tell me the corresponding link? No, I don't have any code for this. Should be trivial though. But the issue is that the update would probably have to be decoupled from CFS load_balance (update_group_capacity()) and the use cases in RT/DL are only valid for asymmetric CPU capacity systems.