On Tue, 21 Mar 2006, Knut Petersen wrote:
>
> System: AOpen i915GMm-HFS motherboard, kernel 2.6.16
> CPU: Intel(R) Pentium(R) M processor 1.86GHz stepping 08
>
> During startup a BogoMips value of 3730.21 is calculated. That
> should be the correct value for the cpu running at full speed.
That sounds correct. On x86, BogoMips these days is just a measure of how
fast the timestamp counter goes (multiplied by two for totally bogus
reasons), and a Pentium-M should have a fixed-frequency TSC that ticks at
the highest possible frequency of the CPU, regardless of what the real
frequency is.
So your BogoMips of 3730 sounds correct.
> But:
>
> "cat /proc/cpuinfo" on the idle system displays the correct cpu speed, but
> a wrong bogomips value:
>
> cpu MHz : 800.000
> bogomips : 3730.21
No, this is the _right_ bogomips value. Since the TSC is fixed-frequency,
bogomips doesn't change with CPU frequency.
> "cat /proc/cpuinfo" on the busy system displays the correct cpu speed too, but
> again a wrong bogomips value:
>
> cpu MHz : 1867.000
> bogomips : 8705.38
Yeah, looks like cpufreq has (totally incorrectly) scaled up the bogomips
value.
The scaling up should actually happen if the TSC runs at core speed _or_
if bogomips is calculated using the old "decl + jne" loop. So I guess
somebody "fixed" a bug that was a bug on such systems, and broke systems
with a proper fixed-frequency TSC.
DaveJ, does this ring any bells?
Linus
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