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Sat, 19 Sep 2026 03:24:22 -0700 (PDT) From: Kayra Cizmeci To: albin_yang@163.com Cc: albinwyang@tencent.com, bsegall@google.com, dietmar.eggemann@arm.com, juri.lelli@redhat.com, kprateek.nayak@amd.com, linux-kernel@vger.kernel.org, mgorman@suse.de, mingo@redhat.com, peterz@infradead.org, rostedt@goodmis.org, vincent.guittot@linaro.org, vschneid@redhat.com Subject: Re: [PATCH] sched/stats: Fix run_delay over-count for migrated sched_delayed tasks Date: Sat, 19 Sep 2026 13:24:20 +0300 Message-ID: <20260919102420.108000-1-kayracizmeci@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260909133345.1572954-1-albin_yang@163.com> References: <20260909133345.1572954-1-albin_yang@163.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit > With DELAY_DEQUEUE, a blocked task stays on the runqueue with > se.sched_delayed set and its sched_info.last_queued is cleared, so the sleep > is not counted into run_delay. > When such a delayed (sleeping) task is migrated across CPUs via the plain > migration paths (move_queued_task / move_queued_task_locked, the latter used > by __migrate_swap_task), activate_task(dst, 0) calls enqueue_task() without > ENQUEUE_RESTORE, re-arming last_queued to the migration timestamp while the > task is still sleeping. The later real wakeup (ENQUEUE_DELAYED) tries to > re-arm last_queued at wakeup time but is suppressed because last_queued is > already non-zero, so sched_info_arrive() folds the whole sleep duration > between migration and wakeup into run_delay. > Fix by not re-arming last_queued for a sched_delayed task in > sched_info_enqueue(). The wakeup path clears sched_delayed before reaching > sched_info_enqueue(), so it still re-arms at the real wakeup time. Plain > runnable tasks and load-balance migrations are unaffected (sched_delayed > tasks are excluded from active load balancing). No? can_migrate_task() skips delayed tasks unless they are both delayed and migration_type not equals migrate_load. And can_migrate_task() is called from detach_one_task() which gets called from active_load_balance_cpu_stop(), with a custom env where the migration type is not set. That means, the migration type is migrate_load, and can_migrate_task() can return 1 for delayed tasks on this path. > Fixes: 152e11f6df29 ("sched/fair: Implement delayed dequeue") > Signed-off-by: Wei Yang Thanks, Kayra :>