Messages in this thread | | | Date | Tue, 18 Nov 2008 17:05:42 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86: Support always running TSC on Intel CPUs |
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* 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
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