Re: [PATCH 3/4] sched: introduce synchronized idle injection

From: Jacob Pan
Date: Tue Jan 19 2016 - 13:01:57 EST

On Tue, 19 Jan 2016 13:06:05 +0100
Ingo Molnar <mingo@xxxxxxxxxx> wrote:

> > If we just look at 20% forced idle, I can see significantly more
> > deep package C-states(PC7) residency.
> > Pkg%pc2 Pkg%pc6 Pkg%pc7
> > w/o patch 3.17 4.39 13.21
> > w/ patch 1.15 1.43 17.24
> Can this be translated to: "this patch improved power efficiency
> (watts per second) by XYZ percent?", with XYZ filled in accordingly?

With CPU bound workload and 20% idle injection ratio, this patch
improves performance per watt by 3.2% on Ivy Bridge system with
Package C7 as the deepest idle.

The above packages C-state residency explains why, i.e. more deeper PC7
when tick is stopped.

With newer CPUs, this improvements should be more visible in that
low power package C-states are getting deeper/less power. I will test
on Skylake client as soon as I have time.