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Date: Wed, 14 May 2008 06:55:58 -0700
From: Arjan van de Ven <arjan@infradead.org>
To: Andi Kleen <andi@firstfloor.org>
Cc: Vegard Nossum <vegard.nossum@gmail.com>, Ingo Molnar <mingo@elte.hu>,
       Thomas Gleixner <tglx@linutronix.de>,
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       "=?UTF-8?B?Uy7Dh2Fn?=(lar Onur" <caglar@pardus.org.tr>,
       Valdis.Kletnieks@vt.edu, Matt Mackall <mpm@selenic.com>,
       linux-kernel@vger.kernel.org, lenb@kernel.org
Subject: Re: [BISECTED] Lots of "rescheduling IPIs" in powertop
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On Wed, 14 May 2008 08:58:05 +0200
> > If the bios says mwait is usable, we need to use it with the values
> > IT gives us.
> 
> At least to my knowledge the ACPI FADT just says what C states are
> available, not if they are implemented with MWAIT or using IO ports.

_CST does; which is what the mwait C-state selection code uses.

(and we've seen quirky systems where C1 mwait didn't work, SMM did
something wrong or something, because the other OS doesn't seem to use
it for that, so making it the default is not really an option)