Messages in this thread | | | Date | Thu, 20 Dec 2007 10:32:05 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH] x86: Voluntary leave_mm before entering ACPI C3 |
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Arjan van de Ven wrote: > On Thu, 20 Dec 2007 08:16:54 -0800 > "H. Peter Anvin" <hpa@zytor.com> wrote: > >> Arjan van de Ven wrote: >>> On Wed, 19 Dec 2007 11:48:14 -0800 >>> "H. Peter Anvin" <hpa@zytor.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) >
Oh, right. My bad.
Of course C3 doesn't guarantee cache retention, only cache coherency.
-hpa
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