sched/fair: Fix PELT integrity for new groups
Vincent reported that when a new task is moved into a new cgroup it gets attached twice to the load tracking: sched_move_task() task_move_group_fair() detach_task_cfs_rq() set_task_rq() attach_task_cfs_rq() attach_entity_load_avg() se->avg.last_load_update = cfs_rq->avg.last_load_update // == 0 enqueue_entity() enqueue_entity_load_avg() update_cfs_rq_load_avg() now = clock() __update_load_avg(&cfs_rq->avg) cfs_rq->avg.last_load_update = now // ages load/util for: now - 0, load/util -> 0 if (migrated) attach_entity_load_avg() se->avg.last_load_update = cfs_rq->avg.last_load_update; // now != 0 The problem is that we don't update cfs_rq load_avg before all entity attach/detach operations. Only enqueue_task() and migrate_task() do this. By fixing this, the above will not happen, because the sched_move_task() attach will have updated cfs_rq's last_load_update time before attach, and in turn the attach will have set the entity's last_load_update stamp. Note that there is a further problem with sched_move_task() calling detach on a task that hasn't yet been attached; this will be taken care of in a subsequent patch. Reported-by: NVincent Guittot <vincent.guittot@linaro.org> Tested-by: NVincent Guittot <vincent.guittot@linaro.org> Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Yuyang Du <yuyang.du@intel.com> Cc: linux-kernel@vger.kernel.org Signed-off-by: NIngo Molnar <mingo@kernel.org>
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