Messages in this thread |  | | | Date | Tue, 18 Nov 2008 11:54:33 -0500 | | From | Joe Korty <> | | Subject | Re: [PATCH] x86: Support always running TSC on Intel CPUs |
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On Tue, Nov 18, 2008 at 11:47:35AM -0500, Pallipadi, Venkatesh wrote: > >>-----Original Message----- >>From: Ingo Molnar [mailto:mingo@elte.hu] >>Sent: Tuesday, November 18, 2008 8:06 AM >>To: Joe Korty >>Cc: Pallipadi, Venkatesh; H Peter Anvin; Thomas Gleixner; linux-kernel >>Subject: Re: [PATCH] x86: Support always running TSC on Intel CPUs >> >>* Joe Korty <joe.korty@ccur.com> wrote: >>> On Tue, Nov 18, 2008 at 09:09:52AM +0100, Ingo Molnar wrote: >>>> * Venki Pallipadi <venkatesh.pallipadi@intel.com> wrote: >>>> >>>> > + if (c->x86_power & (1 << 8)) { >>>> > set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC); >>>> > + set_cpu_cap(c, X86_FEATURE_NOSTOP_TSC); >>>> > + } >>>> >>>> hm, the naming is a bit confusing. We now have 3 variants: >>>> >>>> X86_FEATURE_TSC >>>> X86_FEATURE_CONSTANT_TSC >>>> X86_FEATURE_NOSTOP_TSC >>>> >>>> NOSTOP_TSC is basically what CONSTANT_TSC should have been >>to begin >>>> with ;-) >>>> >>>> i'd suggest to rename it to this: >>>> >>>> X86_FEATURE_TSC >>>> X86_FEATURE_CONSTANT_FREQ_TSC >>>> X86_FEATURE_STABLE_TSC >>>> >>>> ... with CONSTANT_FREQ_TSC not having any real role in the long run. >>>> (it's similarly problematic to a completely unstable TSC) >>>> >>>> does this sound ok? >>> >>> >>> To me, the new naming has the same head-scratching potential >>> as the old.... >>> >>> How about: >>> >>> X86_FEATURE_TSC >>> X86_FEATURE_STABLE_TSC_OBSOLETE >>> X86_FEATURE_STABLE_TSC >> >>the _honest_ naming would be: >> >> X86_FEATURE_TSC >> X86_FEATURE_STABLE_TSC_BUT_NOT_ALWAYS >> X86_FEATURE_STABLE_TSC >> >>;-) >> >>what's head-scratching about X86_FEATURE_CONSTANT_FREQ_TSC? It's a >>limited TSC variant: it follows a reference frequency that does not >>change with cpufreq changes, but it can stop at a whim in C states. So >>it's not "stable" nor really "constant" in the everyday sense. >> > > I don't like STABLE_TSC_OBSOLETE as it does not say anything > descriptive about what it means and people have to look at the code > to find out. > > My original intention was to split this into two features > - P/T state invariant TSC which counts at constant rate > - C-state invariant TSC that never stops > Some CPUs will have only first feature. Others may have both. > > But, I agree it is confusing. > > How about? > X86_FEATURE_FIXEDFREQ_MAYSTOP_TSC > X86_FEATURE_ALWAYS_RUNNING_TSC > > Thanks, > Venki
Much nicer... Regards, Joe
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