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Date: Tue, 18 Jul 2017 20:55:06 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Arjan van de Ven <arjan@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>,
        "Li, Aubrey" <aubrey.li@linux.intel.com>,
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Subject: Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods
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On Mon, Jul 17, 2017 at 12:48:38PM -0700, Arjan van de Ven wrote:
> On 7/17/2017 12:23 PM, Peter Zijlstra wrote:
> > Of course, this all assumes a Gaussian distribution to begin with, if we
> > get bimodal (or worse) distributions we can still get it wrong. To fix
> > that, we'd need to do something better than what we currently have.
> > 
> 
> fwiw some time ago I made a chart for predicted vs actual so you can sort
> of judge the distribution of things visually
> 
> http://git.fenrus.org/tmp/linux2.png

That shows we get it wrong a lot of times (about 50%, as per the
average) and moving the line has benefit. Since for performance you
really don't want to pick the deeper idle state, so you want to bias
your pick towards a shallower state.

Using the CDF approach you can quantify by how much you want it moved.