Re: gettimeofday() moving backwards

[Pavel Machek <pavel-+ZI9xUNit7I@public.gmane.org>]

Hi!

> I am using linux kernel v2.4.20 with ACPI patch dated 2002-12-05.
> 
> I have noticed that if my processor changes state (800Mhz up to 1200Mhz say)
> then gettimeofday() behaves weirdly.  It runs smoothly but every now and again
> (on the order of 10 times a second) it makes a correction.  If I have gone from
> 800Mhz to 1200Mhz then the correction is backwards, otherwise it makes a forward
> jump..
> 
> I presume that this is because the kernel hasn't noticed that the cpu state has
> changed and hasn't corrected the variables that control how the time is
> calculated using the tsc.
> 
> Is there a patch for this..?  It doesn't sound like *too* big a thing.. ie just
> recalculate a cpl of timing variables when the cpu state changes.. but ofc I
> don't know the details :)

Its actually pretty hard to do... Because at least at APM cpu can
change clock any time. And recalibration of delay loop takes quite
long... Still it might be good idea to recalibrate after clock change.

									Pavel
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