Messages in this thread | | | Date | Tue, 18 Nov 2008 11:48:10 -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 11:05:42AM -0500, Ingo Molnar wrote: > > * 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. > > What is 'constant' about it is its reference frequency - hence > X86_FEATURE_CONSTANT_FREQ_TSC. > > Ingo
A name like X86_FEATURE_CONSTANT_FREQ_TSC implies that the result (the TSC) is constant frequency, not the input.
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