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

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Date:	Wed, 11 Dec 2013 14:10:35 +0100
From:	Mike Galbraith <bitbucket@...ine.de>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Len Brown <lenb@...nel.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 Wed, 2013-12-11 at 13:43 +0100, Peter Zijlstra wrote: 
> On Wed, Dec 11, 2013 at 01:29:15PM +0100, Mike Galbraith wrote:
> > On Wed, 2013-12-11 at 12:52 +0100, Peter Zijlstra wrote: 
> > > On Wed, Dec 11, 2013 at 12:38:39PM +0100, Borislav Petkov wrote:
> > > > Right, if it turns out that this is really the case and that this
> > > > erratum hasn't been fixed for models later than 29 - we'd need the
> > > > additional model numbers to set X86_FEATURE_CLFLUSH_MONITOR correctly.
> > > 
> > > You also need: https://lkml.org/lkml/2013/11/19/143
> > > 
> > > Because obviously not all mwait idle loops check that cpu bit.
> > 
> > I had tried that patch, to see if it would magically make the thing
> > start working, nope.  I had also tried...
> 
> > +		if (this_cpu_has(X86_FEATURE_CLFLUSH_MONITOR))
> > +			clflush((void *)&current_thread_info()->flags);
> 
> Yeah, you need a bit extra to enable that feature bit for your CPU as
> bpetkov said.

Works for me, one more for the stable bucket.

So as soon as Len resurrects mwait_idle for Q6600 (and other core2 when
booted max_cstates=1 so tsc clocksource is used instead of pos hpet),
all the (known) idle regressions should be history.

-Mike

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