Messages in this thread | | | Date | Tue, 10 May 2011 08:13:05 -0700 | From | Greg KH <> | Subject | Re: [Stable-review] [12/28] x86, cpu: Clean up AMD erratum 400 workaround |
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On Tue, May 10, 2011 at 04:02:19PM +0200, Borislav Petkov wrote: > On Tue, May 10, 2011 at 08:58:59AM -0400, Ben Hutchings wrote: > > I read that: > > > > " > > Support for Always Running APIC timer (ARAT) was introduced in > > commit db954b5898dd3ef3ef93f4144158ea8f97deb058. This feature > > allows us to avoid switching timers from LAPIC to something else > > (e.g. HPET) and go into timer broadcasts when entering deep > > C-states. > > > > AMD processors don't provide a CPUID bit for that feature but > > they also keep APIC timers running in deep C-states (except for > > cases when the processor is affected by erratum 400). Therefore > > we should set ARAT feature bit on AMD CPUs. > > " > > > > This implies that the HPET was previously used during deep C-states, and > > that all this erratum checking is about deciding whether the CPU has > > ARAT. So what bug is being fixed by using ARAT instead of the HPET? > > That's a good question, actually. The original upstream commit > b87cf80af3ba4b4c008b4face3c68d604e1715c6 wasn't tagged for stable and > Boris O. didn't send it to stable either, as I'm being told. > > Maybe Greg has an idea?
I added it because it was needed to get another errata patch to apply properly, and I saw no reason not to apply other "quirks" like this to older kernels, right?
Or should I not have done that?
thanks,
greg k-h
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