Re: [PATCH] x86: Voluntary leave_mm before entering ACPI C3

[H. Peter Anvin]

Arjan van de Ven wrote:
> On Thu, 20 Dec 2007 08:16:54 -0800
> "H. Peter Anvin" <hpa@xxxxxxxxx> wrote:
>
> > Arjan van de Ven wrote:
> > > On Wed, 19 Dec 2007 11:48:14 -0800
> > > "H. Peter Anvin" <hpa@xxxxxxxxx> 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)

Oh, right.  My bad.

Of course C3 doesn't guarantee cache retention, only cache coherency.

	-hpa
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