On 11/16/23 13:07, Abel Wu wrote:
On 11/16/23 12:48 PM, Abel Wu Wrote:I lost the fact that we'll update_min_vruntime() every time we update_curr(). Because of this fact, we can indeed wait until we need the correct min_vruntime and update_min_vruntime() then. The only consideration that I came up with is that the sched_debug may not be able to reflect the accurate min_vruntime in time. But this may not be a big problem.
On 11/15/23 11:36 PM, Yiwei Lin Wrote:
@@ -3712,8 +3811,17 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,Sorry if I am asking stupid question...... It looks like reweight_entity() may have chance to change the weight of cfs_rq->curr entity, but we'll never update_min_vruntime() when reweighting it. Is there any reason that we can skip the update_min_vruntime() for this case?
enqueue_load_avg(cfs_rq, se);
if (se->on_rq) {
update_load_add(&cfs_rq->load, se->load.weight);
- if (cfs_rq->curr != se)
- avg_vruntime_add(cfs_rq, se);
+ if (!curr) {
+ /*
+ * The entity's vruntime has been adjusted, so let's check
+ * whether the rq-wide min_vruntime needs updated too. Since
+ * the calculations above require stable min_vruntime rather
+ * than up-to-date one, we do the update at the end of the
+ * reweight process.
+ */
+ __enqueue_entity(cfs_rq, se);
+ update_min_vruntime(cfs_rq);
+ }
}
}
No, you are right!
I was intended to update_min_vruntime() if se->on_rq and no matter
it is curr or not, just as you suggested. But after a second thought
I wonder if it is necessary to update *NOW*, since we will always
update_curr() before making any change to cfs_rq. Thoughts?
Further, I have another advanced thought we can remove the update_min_vruntime() here in the reweight_entity() directly to save more time. The reason that I think this is because min_vruntime is not for normalization of vruntime as before which is required on CFS, so we will always update_curr() for the latest min_vruntime before using it. Also, the update_min_vruntime() in dequeue_entity() may also be removed as the reason, i.e. just do update_min_vruntime() in update_curr() to simplify. What do you think?