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Subject: Re: 50 Watt idle power regression bisected to Linux-3.10
From: Mike Galbraith <bitbucket@online.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>, Thomas Gleixner <tglx@linutronix.de>,
        Len Brown <lenb@kernel.org>, Linux PM list <linux-pm@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Jeremy Eder <jeder@redhat.com>, x86@kernel.org
Date: Wed, 11 Dec 2013 14:10:35 +0100
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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