On Tue, May 10, 2011 at 08:13:05AM -0700, Greg KH wrote: > 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?
Nah, I wouldn't say that. While this patch doesn't directly fix a regression, it does away with the erratum 400 workaround where we switch to HPET so it is more or less a regression fix for current and future machines which aren't affected by that erratum. Besides reading the LAPIC is much cheaper so we should be getting even a slight performance bump with it. So no, I don't see a problem with the patch being in stable. Thanks. -- Regards/Gruss, Boris. Advanced Micro Devices GmbH Einsteinring 24, 85609 Dornach General Managers: Alberto Bozzo, Andrew Bowd Registration: Dornach, Gemeinde Aschheim, Landkreis Muenchen Registergericht Muenchen, HRB Nr. 43632 _______________________________________________ stable mailing list [email protected] http://linux.kernel.org/mailman/listinfo/stable
