On 07/11/2018 01:09 AM, Joel Fernandes wrote:
On Mon, Jul 09, 2018 at 05:47:53PM +0100, Dietmar Eggemann wrote:
A CFS (SCHED_OTHER, SCHED_BATCH or SCHED_IDLE policy) task's
se->runnable_weight must always be in sync with its se->load.weight.

se->runnable_weight is set to se->load.weight when the task is
forked (init_entity_runnable_average()) or reniced (reweight_entity()).

There are two cases in set_load_weight() which since they currently only
set se->load.weight could lead to a situation in which se->load.weight
is different to se->runnable_weight for a CFS task:

(1) A task switches to SCHED_IDLE.

(2) A SCHED_FIFO, SCHED_RR or SCHED_DEADLINE task which has been reniced
     (during which only its static priority gets set) switches to
     SCHED_OTHER or SCHED_BATCH.

Set se->runnable_weight to se->load.weight in these two cases to prevent
this. This eliminates the need to explicitly set it to se->load.weight
during PELT updates in the CFS scheduler fastpath.

Looks good to me. By the way just asking, is there a chance where
se_weight(se) and se_runnable(se) can ever be different?

Yes they can be different, not for a task though but for se's representing task groups. It got introduced to be able to propagate load and runnable load independently through the task groups hierarchies.

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