linux-kernel - Re: [PATCH] x86: Voluntary leave

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Message-ID: <20071220102202.64f395a7@laptopd505.fenrus.org>
Date:	Thu, 20 Dec 2007 10:22:02 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Venki Pallipadi <venkatesh.pallipadi@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Len Brown <lenb@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: Voluntary leave_mm before entering ACPI C3

On Thu, 20 Dec 2007 08:16:54 -0800
"H. Peter Anvin" <hpa@...or.com> wrote:

> Arjan van de Ven wrote:
> > On Wed, 19 Dec 2007 11:48:14 -0800
> > "H. Peter Anvin" <hpa@...or.com> wrote:
> > 
> >> I think C3 guarantees that the cache contents stay intact, and thus
> >> it might make sense in some technology to preserve the TLB as well
> >> (being a kind of cache.)
> > 
> > that sounds nice. It's fiction though ;-)
> > 
> > The thing to realize is that linux only sees "ACPI C3"; the BIOS
> > maps that C3 to.. well any of the C states the processor in the
> > system has. What you're saying is afaik correct for the *hardware*
> > C3, not for the "C3" that Linux sees..
> > 
> 
> Well, it can only map ACPI C3 to a state which is no more "dead" than 
> what would normally be permitted by C3.  IIRC, C3 is allowed to
> require that DMA be turned off (unlike C2), but is not allowed to
> lose the CPU state.

state isn't lost if the tlb or the caches are flushed... 
(properly, eg all pending writebacks are written back first etc)


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