Messages in this thread | | | Date | Tue, 23 Apr 2019 12:30:34 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH 2/2] x86/tsc: set LAPIC timer frequency to crystal clock frequency |
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* Daniel Drake <drake@endlessm.com> wrote:
> On Mon, Apr 22, 2019 at 8:04 PM Ingo Molnar <mingo@kernel.org> wrote: > > Minor style nit: the parentheses are unnecessary, integer expressions > > like this are evaluated left to right and multiplication and division has > > the same precedence. > > Fair point, although the same could be said for cpu_khz_from_msr().
Yes, this standardization on mhz, if it makes sense, might have to be propagated a bit to function names and any other variables.
Another naming quirk: what unit is 'lapic_timer_frequency' in? AFAICS it's a "period" unit (number of clock cycles per jiffy), not a frequency (which is number of cycles per second) - so the better name might be lapic_timer_period?
> > But it might also make sense to actually store crystal_mhz instead of > > crystal_khz, because both CPUID 15H and 16H provides MHz values. > > > > That way the above expression would simplify to: > > > > lapic_timer_frequency = crystal_mhz / HZ; > > Wouldn't it be > lapic_timer_frequency = crystal_mhz * 1000000 / HZ; > ?
Sorry, what I wanted to suggest is crystal_hz, not crystal_mhz.
I.e. store the raw unit that comes out of the CPUID, which appears to be HZ, right?
That would change the calculation to:
lapic_timer_period = crystal_hz / HZ;
Note how clearly it's visible in that calculation that what we calculate there is a 'period', not a frequency.
Thanks,
Ingo
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