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Fri, 06 Nov 2026 10:05:43 -0800 (PST) Received: from scheduler.schedules ([85.100.66.184]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4b572caf48bsm171361085e9.11.2026.11.06.10.05.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Nov 2026 10:05:42 -0800 (PST) Date: Fri, 6 Nov 2026 21:05:38 +0300 From: Kayra Cizmeci To: Vincent Guittot Cc: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com, linux-kernel@vger.kernel.org, lukasz.luba@arm.com, rafael@kernel.org, linux-pm@vger.kernel.org, tj@kernel.org, void@manifault.com, arighi@nvidia.com, changwoo@igalia.com, sched-ext@lists.linux.dev, qyousef@layalina.io, christian.loehle@arm.com, pierre.gondois@arm.com, sshegde@linux.ibm.com, tim.c.chen@linux.intel.com Subject: Re: [PATCH 03/20 v3] sched/eevdf: Reset lag at wakeup when migrating and prev has been idle Message-ID: References: <20261106151947.3991524-1-vincent.guittot@linaro.org> <20261106151947.3991524-4-vincent.guittot@linaro.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20261106151947.3991524-4-vincent.guittot@linaro.org> On Fri, Nov 06, 2026 at 04:19:30PM +0100, Vincent Guittot wrote: > When prev CPU entered idle while a task was sleeping, we assume that the > latter received enough running time and the lag can be cleared similarly to > what happens for a negative lag. > While migrating the waking task to a new cpu, Check if prev CPU entered > idle in the meantime. > > Signed-off-by: Vincent Guittot > --- > kernel/sched/fair.c | 27 +++++++++++++++++++++++++++ > 1 file changed, 27 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 79f53811274e..945de0215abb 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -932,6 +932,27 @@ bool update_entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se) > static inline unsigned long cfs_rq_load_avg(struct cfs_rq *cfs_rq); > static unsigned long task_h_load(struct task_struct *p); > > +static __always_inline > +void entity_clear_lag(struct task_struct *p) > +{ > + struct sched_entity *se; > + struct cfs_rq *cfs_rq; > + > + if (READ_ONCE(p->__state) != TASK_WAKING) > + return; > + > + se = &p->se; > + /* Negative lag implies delayed dequeue */ > + if (se->vlag <= 0) > + return; > + > + cfs_rq = &task_rq(p)->cfs; > + > + /* CPU has been idle in between so the lag has been removed */ > + if (se->vlag_seq != READ_ONCE(cfs_rq->idle_seq)) > + se->vlag = 0; > +} > + > static __always_inline > void decay_entity_lag(struct cfs_rq *cfs_rq, struct task_struct *p, int flags) > { > @@ -10049,6 +10070,12 @@ static void migrate_task_rq_fair(struct task_struct *p, int new_cpu) > struct sched_entity *se = &p->se; > > if (!task_on_rq_migrating(p)) { > + /* > + * Clear the positive lag of a waking task before migrating to > + * the new cpu. > + */ > + entity_clear_lag(p); > + > remove_entity_load_avg(se); > > /* > -- > 2.53.0 > Yeah well looks good. I need to test this on my head tho: CPU1: CPU2: TA TD TB TC Let's say TA sleeps and has 12 lags. And while its sleeping TB and TC leaves: CPU1: TA (Sleeping) Then some new tasks come: CPU1: TA (Sleeping) TW TR Now TA wakes up, we enter try_to_wake_up(), from there we pick CPU2 and enter set_task_cpu(), from there migrate_task_rq_fair(), and to entity_clear_lag(). And from there this just works correctly. Reviewed-by: Kayra Cizmeci Cheers, Kayra