On Thu, 2006-06-29 at 19:15 +0200, Fernando Apesteguía wrote:
> Thanks to both of you.
>
> If I use jiffies global variable, very often I get two identical
> values before and after the function call. I need more accurate
> stamps. Now, with rdtscll I get these values but in cycles. This
> measurement is for the same machine, so if I could have the cpu MHz I
> could do the division. Am I right?
>
> Now the question is how to get cpu MHz. The cpuinfo_x86 structure has
> not this field. I try to keep track for the value showed
> by /proc/cpuinfo. But at arc/i383/kernel/cpu/proc.c I see the
> following sentence:
>
> if ( cpu_has(c, X86_FEATURE_TSC) ) {
> seq_printf(m, "cpu MHz\t\t: %u.%03u\n",
> cpu_khz / 1000, (cpu_khz % 1000));
>
> But cpu_khz is not declared in this file.... even as extern.
>
> Any ideas to get cpu MHz (or KHz) in order to convert cycles to time
> units?
it'll be in a header
BUT
cpu_khz is NOT a constant.. power management will change the actual
frequency all the time..
and.. as I said, some processors entirely stop the tsc in the idle
loop..
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