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Thu, 18 Aug 2022 04:03:17 -0700 (PDT) Received: from [10.70.253.98] ([139.177.225.230]) by smtp.gmail.com with ESMTPSA id q5-20020a170902a3c500b0016befc83c6bsm1104176plb.165.2022.08.18.04.03.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 18 Aug 2022 04:03:17 -0700 (PDT) Message-ID: <0df80a63-5d1b-744e-d143-d2b0ccc52cd5@bytedance.com> Date: Thu, 18 Aug 2022 19:03:11 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.1.2 Subject: Re: [PATCH v5 8/9] sched/fair: defer task sched_avg attach to enqueue_entity() Content-Language: en-US To: Peter Zijlstra Cc: vincent.guittot@linaro.org, dietmar.eggemann@arm.com, mingo@redhat.com, rostedt@goodmis.org, bsegall@google.com, vschneid@redhat.com, linux-kernel@vger.kernel.org, tj@kernel.org References: <20220818034343.87625-1-zhouchengming@bytedance.com> <20220818034343.87625-9-zhouchengming@bytedance.com> From: Chengming Zhou In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/8/18 18:39, Peter Zijlstra wrote: > On Thu, Aug 18, 2022 at 11:43:42AM +0800, Chengming Zhou wrote: >> When wake_up_new_task(), we would use post_init_entity_util_avg() >> to init util_avg/runnable_avg based on cpu's util_avg at that time, >> then attach task sched_avg to cfs_rq. >> >> Since enqueue_entity() would always attach any unattached task entity, >> so we can defer this work to enqueue_entity(). >> >> post_init_entity_util_avg(p) >> attach_entity_cfs_rq() --> (1) >> activate_task(rq, p) >> enqueue_task() := enqueue_task_fair() >> enqueue_entity() >> update_load_avg(cfs_rq, se, UPDATE_TG | DO_ATTACH) >> if (!se->avg.last_update_time && (flags & DO_ATTACH)) >> attach_entity_load_avg() --> (2) >> >> This patch defer attach from (1) to (2) >> >> Signed-off-by: Chengming Zhou >> --- >> kernel/sched/fair.c | 4 ---- >> 1 file changed, 4 deletions(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index e0d34ecdabae..aacf38a72714 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -799,8 +799,6 @@ void init_entity_runnable_average(struct sched_entity *se) >> /* when this task enqueue'ed, it will contribute to its cfs_rq's load_avg */ >> } >> >> -static void attach_entity_cfs_rq(struct sched_entity *se); >> - >> /* >> * With new tasks being created, their initial util_avgs are extrapolated >> * based on the cfs_rq's current util_avg: >> @@ -863,8 +861,6 @@ void post_init_entity_util_avg(struct task_struct *p) >> se->avg.last_update_time = cfs_rq_clock_pelt(cfs_rq); >> return; >> } >> - >> - attach_entity_cfs_rq(se); >> } > > There are comments with update_cfs_rq_load_avg() and > remove_entity_load_avg() that seem to rely on post_init_entity_util() > doing this attach. > > If that is no longer true; at the very least those comments need to be > updated, but also, I don't immediately see why that's no longer the > case, so please explain. This attach in post_init_entity_util() will be done in enqueue_entity() -> update_load_avg(cfs_rq, se, UPDATE_TG | DO_ATTACH) loop. So these comments should be updated in the next version. Thanks!