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

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Message-ID: <20151105113235.1b98d79c@icelake>
Date:	Thu, 5 Nov 2015 11:32:35 -0800
From:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Paul Turner <pjt@...gle.com>, Len Brown <len.brown@...el.com>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Andi Kleen <andi.kleen@...el.com>,
	Rafael Wysocki <rafael.j.wysocki@...el.com>
Subject: Re: [RFC PATCH 3/3] sched: introduce synchronized idle injection

On Thu, 5 Nov 2015 11:27:32 -0800
Jacob Pan <jacob.jun.pan@...ux.intel.com> wrote:

> On Thu, 5 Nov 2015 11:09:22 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > > Before:
> > > CPU0 ______||| ||  |___________| || || |_____
> > > CPU1 _________||| ||  |_______| || |_______
> > > 
> > > After:
> > > 
> > > CPU0 ______||| ||  |___________| || || |_____
> > > CPU1 ______||| ||  |___________| || |_______
> > > 
> > > The goal is to have overlapping idle time if the load is already
> > > balanced. The energy saving can be significant.  
> > 
> > I can see such a scheme having a fairly big impact on latency, esp.
> > with forced idleness such as this. That's not going to be popular
> > for many workloads.
> agreed, it would be for limited workload. the key is to identify such
> workloads at runtime. I am thinking to use the load average of
> the busiest CPU as reference for consolidation, will not go beyond
> that.
> For the patch I have today and if you play a game like this one
> http://www.agame.com/game/cut-the-rope
sorry, hit the wrong button before finishing the email.
and set duration to 5, and 20% idle, it does not affect user experience
much. It saves ~15% power on my BDW ultrabook. Other unbalanced
workload such as video playback don't benefit, should be avoided.
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