Re: [PATCH 1/4] sched/eevdf: Fix vruntime adjustment on reweight

[Tianchen Ding <dtcccc@linux.alibaba.com>]

Hi Abel:

I'm not so familiar with eevdf and still learning. Here I've some questions 
about this patch.

1. You did proof that V will not change during reweight (COROLLARY #2). However, 
according to the original paper, the new V will be:
V' = V + lag(j)/(W - w_j) - lag(j)/(W - w_j + w'_j)
So the V' in paper will change (when lag is not zero).
Is the V in Linux code slightly different from the paper?

2. I print some log around reweight_entity(), mainly want to print V by calling 
avg_vruntime(cfs_rq). I found your algorithm only keeps the V unchanged during 
reweight_eevdf(), but not reweight_entity().

In detail:
If curr is true (i.e., cfs_rq->curr == se), we will directly run 
reweight_eevdf(), and the V is not changed.
If curr is false, we will have __dequeue_entity() -> reweight_eevdf() -> 
__enqueue_entity(). The V is finally changed due to dequeue and enqueue. So the 
result of reweight_entity() will be impacted by "cfs_rq->curr == se", is this 
expected?

Thanks!