Re: [PATCH v5 1/4] sched/fair: add util_est on top of PELT

[Peter Zijlstra]

On Wed, Mar 07, 2018 at 11:31:49AM +0000, Patrick Bellasi wrote:
> > It appears to me this isn't a stable situation and completely relies on
> > the !nr_running case to recalibrate. If we ensure that doesn't happen
> > for a significant while the sum can run-away, right?
> 
> By away you mean go over 1024 or overflow the unsigned int storage?

the later, I think you can make it arbitrarily large. Have a busy task
on CPU0, this ensure !nr_running never happens.

Start a busy task on CPU1, wait for it to hit u=1, then migrate it to
CPU0, then wait for it to hit u=.5 then kill it, this effectively adds
.5 to the enqueued value, repeat indefinitely.