Re: [-rt] time-related problems with CPU frequency scaling

[Lee Revell]

On Sun, 2006-04-16 at 20:41 +0200, Wolfgang Hoffmann wrote:
> - if CPU frequency is low when jackd is started, it complains:
>     "delay of 2915.000 usecs exceeds estimated spare
>     time of 2847.000; restart ..."
>   as soon as frequency is scaled up. Seems that jackd gets confused by some
>   influence of CPU frequency on timekeeping? No problems as long as CPU
>   frequency isn't scaled up, though.

JACK still uses the TSC for timing and thus is incompatible with CPU
frequency scaling.  You must use the -clockfix branch from CVS.

> - values in /proc/sys/kernel/preempt_max_latency scales inverse to
>     CPU frequency, i.e. 24us with CPU @ 800MHz and 12us with CPU @ 1,6GHz 

This is normal - code that takes 12us to run at 1.6 GHz will take 24us
at 800MHz.  TANSTAAFL ;-)

Lee

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