Re: [PATCH 04/18] Make cpu_tsc_khz updates use local CPU

[Zachary Amsden]

On 07/19/2010 10:53 PM, Avi Kivity wrote:
> On 07/19/2010 11:06 PM, Zachary Amsden wrote:
> > > > +static void tsc_khz_changed(void *data)
> > > >   {
> > > > -    /* nothing */
> > > > +    struct cpufreq_freqs *freq = data;
> > > > +    unsigned long khz = 0;
> > > > +
> > > > +    if (data)
> > > > +        khz = freq->new;
> > > > +    else if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
> > > > +        khz = cpufreq_quick_get(raw_smp_processor_id());
> > > > +    if (!khz)
> > > > +        khz = tsc_khz;
> > > > +    __get_cpu_var(cpu_tsc_khz) = khz;
> > > >   }
> > >
> > > Do we really need to cache cpufreq_quick_get()?  If it's really 
> > > quick, why not just use it everywhere instead of cacheing it?  Not a 
> > > comment on this patch.
> >
> >
> > If cpufreq is compiled in, but disabled, it returns zero, so we need 
> > some sort of logic.
>
> Maybe it's better to put it into cpufreq_quick_get().  Inconsistent 
> APIs that appear to work are bad.

I don't think it's quite so simple; cpufreq is platform independent and 
tsc_khz is a platform specific export.  It seems cpufreq is designed to 
return zero when disabled and we're the unusual ones for wanting to use it.

Zach
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