Messages in this thread | | | Subject | Re: [PATCH] sched/fair: Remove setting task's se->runnable_weight during PELT update | From | Dietmar Eggemann <> | Date | Fri, 13 Jul 2018 16:57:46 +0200 |
| |
On 07/12/2018 10:17 AM, Joel Fernandes wrote: > On Wed, Jul 11, 2018 at 10:43:28AM +0200, Dietmar Eggemann wrote: >> 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. > > I know that task-group se has different values. I was saying for task ses, > the extra division can be skipped possibly improving performance (if at all).
Ah, OK, I didn't pay attention to the '... if the sa belongs to the task:' part.
Since ___update_load_sum() is either called with !!se->on_rq or 0 for both ('load' and 'runnable'), sa->load_sum and sa->runnable_load_sum should be equal for a task.
And since se_weight(se) and se_runnable(se) for 'load' and 'runnable' of ___update_load_avg() are the same for a task, sa->load_avg and sa->runnable_load_avg should be also equal for a task.
You would have to pass the information that sa belongs to a se and not to a cfs_rq into ___update_load_avg() though to be able to use entity_is_task().
[...]
| |