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

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Date:	Tue, 19 Jan 2016 10:00:27 -0800
From:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	John Stultz <john.stultz@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Len Brown <len.brown@...el.com>,
	Rafael Wysocki <rafael.j.wysocki@...el.com>,
	Eduardo Valentin <edubezval@...il.com>,
	Paul Turner <pjt@...gle.com>, jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH 3/4] sched: introduce synchronized idle injection

On Tue, 19 Jan 2016 13:06:05 +0100
Ingo Molnar <mingo@...nel.org> 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.

Thanks,

Jacob