Re: [RFC PATCH 0/8] sched/fair: Propagate load balancing stats up the sched domain hierarchy

[Chen, Yu C]

On 3/18/2025 1:25 AM, Peter Zijlstra wrote:
> On Thu, Mar 13, 2025 at 09:37:38AM +0000, K Prateek Nayak wrote:
> > tl;dr
> >
> > This prototype is currently limited in the sense that it can only reuse
> > statistics for busy load balancing. Reusing stats for newidle load
> > balancing specifically ran into issues elaborated below.
>
> Right, it makes sense for busy load balance, newidle I think:
>
> > David had proposed SHARED_RUNQ [4] to improve on the shortcomings of
> > newidle balance for Meta's production workloads.
>
> we need to look at this again. Something around the EEVDF merge made the
> thing unhappy -- if we figure out what and fix it, I think this makes

Could you give some links on what the issue is? The newly-idle balance 
fail to pull tasks after switching to EEVDF?(I don't
see the connection between EEVDF and newly-idle balance on top of
my head)

> more sense than trying to optimize the current scheme for newidle.
>
> newidle really is about getting *any* work fast, which is a totally
> different game than the regular busy balancing.

The newly idle iterates every CPU in the domain to find the busiest one, 
would the following work: find a relative busy CPU and stop the search, 
say, rq->nr_running >= 2 and also consider the candidate task's average 
duration.

thanks,
Chenyu