On Mon, Sep 12, 2016 at 09:47:52AM +0200, Vincent Guittot wrote:
When a task switches to fair scheduling class, the period between now and the last update of its utilization is accounted as running time whatever happened during this period. This wrong accounting applies to the task and also to the task group branch.
When changing the property of a running task like its list of allowed CPUs or its scheduling class, we follow the sequence: -dequeue task -put task -change the property -set task as current task -enqueue task
The end of the sequence doesn't follow the normal sequence which is : -enqueue a task -then set the task as current task.
This wrong ordering is the root cause of wrong utilization accounting. Update the sequence to follow the right one: -dequeue task -put task -change the property -enqueue task -set task as current task
But enqueue_entity depends on cfs_rq->curr, which is set by set_curr_task_fair().
Also, the normalize comment in dequeue_entity() worries me, 'someone' didn't update that when he moved update_min_vruntime() around.