Re: [PATCH 1/3] sched/fair: Add tg_load_contrib cfs_rq decay checking

From: Odin Ugedal
Date: Thu May 27 2021 - 07:05:03 EST

> 1st : ensure that cfs_rq->load_sum is not null if cfs_rq-> load_isn't too
> 2nd : call update_tg_load_avg() during child update so we will be sure
> to update tg_load_avg_contrib before removing the cfs from the list

Ahh, yeah, with "1st" that would work. Yeah, that was my initial
implementation of the change, but I thought that it was better to keep
the logic away from the "hot path". We can verify this in
update_tg_cfs_load(), and then force update_tg_load_avg() inside
__update_blocked_fair() when avg.load_avg is 0. (Given that this is
the only place where we can end up in this situation. I can update
this patch to do that instead.

Another solution is to update avg.load_avg
inside__update_blocked_fair() when load_sum is 0, and then propagate
that with update_tg_load_avg(). This removes the logic from the hot
path all together.

Not sure what the preferred way is. I have not found any other places
where this situation _should_ occur, but who knows..