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

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Date:	Tue, 10 Dec 2013 12:41:27 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Mike Galbraith <bitbucket@...ine.de>
Cc:	Len Brown <lenb@...nel.org>, Thomas Gleixner <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


* Mike Galbraith <bitbucket@...ine.de> wrote:

> On Sat, 2013-12-07 at 11:45 -0500, Len Brown wrote: 
> > >> It fixes that, except for my Q6600 box.  Too bad mwait_idle() went away,
> > >> beloved old box doesn't play hints game, so it continues to flog itself.
> > 
> > 
> > Thanks for pointing this out, Mike!
> > 
> > A Q6600 is a Kentsfield.  I dug one of those up.
> > Indeed, the only idle capabilities it has are  HALT
> > and old style MWAIT, and the latter is much more effective.
> > running 3.8 it idles at 75 watts.
> > running 3.8 with idle=nomwait it idles at 100 watts,
> > which is what it will do with 3.9 and later due to the patch below.
> > 
> > commit 69fb3676df3329a7142803bb3502fa59dc0db2e3
> > Author: Len Brown <len.brown@...el.com>
> > Date:   Sun Feb 10 01:38:39 2013 -0500
> > 
> >     x86 idle: remove mwait_idle() and "idle=mwait" cmdline param
> > 
> > Kentsfield proves that patch was based on a fault assumption.
> > Sweet box in its day, ECC memory and everything -- probably still
> > a fair number of them running...
> > 
> > Plus, I've found another machine that depends on having an idle=mwait
> > idle loop (A Sony Vaio BIOS SMM code apparently assumes we use it in
> > https://bugzilla.kernel.org/show_bug.cgi?id=60770)
> > 
> > So it looks like I need to (also) restore the simple idle=mwait idle loop
> > to make some machines happy.
> 
> Cool, box will definitely be happier.

I assume old-style MWAIT will be activated automatically on such 
boxes, there's no need to pass in idle=mwait on the boot command line, 
correct?

Thanks,

	Ingo
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