Re: [PATCH v2 2/2] sched_ext: Add cpuperf support

[Tejun Heo <tj@kernel.org>]

Hello,

On Tue, Jul 09, 2024 at 03:36:34PM +0200, Vincent Guittot wrote:
> > I tried this and it's a bit problematic. Migrating out all the tasks do
> > bring the numbers pretty close to zero but the math doesn't work out exactly
> > and it often leaves 1 in the averages. While the fair class is in use, they
> 
> hmm interesting, such remaining small value could be expected for
> load_avg but not with util_avg which is normally a direct propagation.
> Do you have a sequence in particular ?

Oh, I thought it was a byproduct of decay calculations not exactly matching
up between the sum and the components but I haven't really checked. It's
really easy to reproduce. Just boot a kernel with sched_ext enabled (with
some instrumentations added to monitor the util calculation), run some
stress workload to be sure and run a sched_ext scheduler (make -C
tools/sched_ext && tools/sched_ext/build/bin/scx_simple).

Thanks.

-- 
tejun