linux-kernel - Re: 50 Watt idle power regression bisected to Linux-3.10

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Date:	Sun, 08 Dec 2013 05:57:04 +0100
From:	Mike Galbraith <bitbucket@...ine.de>
To:	Len Brown <lenb@...nel.org>
Cc:	tglx@...utronix.de, Peter Zijlstra <peterz@...radead.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jeremy Eder <jeder@...hat.com>, x86@...nel.org
Subject: Re: 50 Watt idle power regression bisected to Linux-3.10

On Sat, 2013-12-07 at 03:00 -0500, Len Brown wrote: 
> Hello Thomas,
> 
> An idle WSM-EX box (40 Xeon cores) runs 50 Watts hotter after this patch:
> 
> commit 7d1a941731fabf27e5fb6edbebb79fe856edb4e5
> Author: Thomas Gleixner <tglx@...utronix.de>
> Date:   Thu Mar 21 22:50:03 2013 +0100
> 
>     x86: Use generic idle loop
> 
> ie. the commit before this patch (aba92c9e2cf3042bf6efc68fa2e4235ba01bf499)
> runs at 50 watts less, as do Linux 3.7, 3.8 and 3.9.
> 
> The difference is that the good kernels allow about 98% residence
> in the package C6 state, while the bad kernel is so noisy that it
> gets into pc6 0% of the time.
> (indeed, even core C6 is reduced to about 50% from over 99%)

FWIW, my little x3550 (E5620) box is spending ~99% of its time in C3 per
powertop, deepest state it has.  It took a big hit from 69a37bea as well
as 7d1a9417, but with revert of 69a37bea, and addition of ea811747, it's
fairly close to 3.7 in fastpath weight, and greenery _seems_ fine.

-Mike

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