Re: [PATCH 01/15] sched/fair: Add avg_vruntime

[Peter Zijlstra]

On Fri, Jun 02, 2023 at 03:51:53PM +0200, Vincent Guittot wrote:
> On Wed, 31 May 2023 at 14:47, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > +static void
> > +avg_vruntime_add(struct cfs_rq *cfs_rq, struct sched_entity *se)
> > +{
> > +       unsigned long weight = scale_load_down(se->load.weight);
> > +       s64 key = entity_key(cfs_rq, se);
> > +
> > +       cfs_rq->avg_vruntime += key * weight;
> > +       cfs_rq->avg_load += weight;
> 
> isn't cfs_rq->avg_load similar to scale_load_down(cfs_rq->load.weight)  ?
> 
> > +}

Similar, yes, but not quite the same in two ways:

 - it's sometimes off by one entry due to ordering of operations -- this
   is probably fixable.

 - it does the scale down after addition, whereas this does the scale
   down before addition, esp for multiple low weight entries this makes
   a significant difference.