calcru: runtime went backwards

[Yuriy Tsibizov]

>> With -CURRENT up to 2006-02-12 06:57:41 UTC (last commit by scottl)
>> I still can see some calcru messages:
>
> Right, but these have much smaller deltas than the other ones you saw.
>
>> calcru: runtime went backwards from 3508844 usec to 3508842 usec for pid 28 (pagezero)
>
> My theory currently is that these are side effects of the cputick
> calibration code:  If the cputick rate gets measured to be a bit higher,
> the next calculation will result in slightly lower numbers for the
> cpu utilization in microseconds and the warning will fire.
>
> This will be particularly easy to trigger on machines with power
> management on (laptops mostly).
>
> My current inclination is to simply not issue this warning if the
> cpu_tick is marked as "variable".
>
> The other side of this is that I've been looking at having the
> ACPI power management code announce the maximum speed of the TSC
> to the cputick code, that would make such machines "fixed frequency"
> cpu_tick machines from the start and even if enabled, this warning
> should not issue in that case.
I have CPU (AMD K6) with TSC, but my motherboard (ASUS TX97) does not 
support ACPI. This combination can also be treated as a "fixed frequency" 
machine.

Yuriy.