Messages in this thread |  | | | Date | Tue, 21 Mar 2006 10:10:48 -0800 (PST) | | From | Linus Torvalds <> | | Subject | Re: [BUG] wrong bogomips values with kernel 2.6.16 |
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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?
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