Re: Re: [Qemu-devel] Timing problems

[Jim C. Brown]

On Mon, Aug 29, 2005 at 10:01:39AM +0700, Mulyadi Santosa wrote:
> Hello...
> 
> > It simply
> > replaces the virtual timer mechanism based on CPU tick count (which
> > is totally messed up in a SpeedStep setting) with calls to the
> > realtime clock. It should work even when emulation is stopped
> > intermittently, I hope, since the  built in "virtual clock stop"
> > mechanism ist left unchanged.
> 
> Hm..... hard choice.....correctness traded for perfomance.... But 
> anyway....IMHO this hack  is needed for every speed-step enabled 
> machine. Perhaps...the other workaround is via cpufreqd? I don't have 
> any Pentium M based PC/laptop around, so this is just a pure guess
> 

The other patch for this just used a constant to increment the time iirc
(based on some value in /proc).

> BTW, your patch seems reversed....if you really mean you want to fetch 
> realtime clock, you should use "rdtsc", right? But the patch seems 
> replaced "rdtsc" with get_clock().... 
> 

The values returned by rdtsc seem to vary depending on cpu frequency when
speedstep is enabled. get_clock() is actually more accurate (tho i think less
precise), at least from the user land POV.

-- 
Infinite complexity begets infinite beauty.
Infinite precision begets infinite perfection.