linux-kernel - Re: acpi_idle: Very idle Core i7 machine never enters C3

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Message-ID: <20100525123701.GA7876@srcf.ucam.org>
Date:	Tue, 25 May 2010 13:37:01 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Len Brown <lenb@...nel.org>
Cc:	Philip Langdale <philipl@...rt.org>,
	Jeff Garrett <jeff@...rrett.org>,
	Andi Kleen <andi@...stfloor.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-acpi@...r.kernel.org, luming.yu@...el.com, venki@...gle.com
Subject: Re: acpi_idle: Very idle Core i7 machine never enters C3

On Tue, May 25, 2010 at 01:43:26AM -0400, Len Brown wrote:

> I'm told by the hardware guys that BM_STS is _not_ always
> a NOP, and so we're not supposed to simply ignore it on C3 --
> though it should be extremely rare that we see it set.
> If it is ever set, it should go on and off depending on 
> activity on some latency sensitive device, like out on the LPC.
> It may be possible for the BIOS writer to configure the chipset
> so that BM_STS is enabled always, presumably to accomodate
> some latency sensitve device -- or maybe by mistake.

On some hardware we've seen BM_STS be enabled approximately 50% of the 
time without any obvious cause.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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