Re: CPUfreq - udelay() interaction issues

[Pavel Machek]

Hi!

> Seems a bit more complicated than what I had in mind. This is
> touching the scheduler I think we can get away without having to.
> Also, there is no simple implementation for the "slowpath" that can
> guarantee the delay without starting over the loop and hoping not to
> get interrupted or just giving up and doing a massively inaccurate
> delay (like msleep, etc).
> 
> I was thinking of something along the lines of this:
> 
> udelay()
> {
>   if (!is_atomic())
> 	down_read(&freq_sem);
>   /* else
> 	do nothing since cpufreq can't interrupt you.
>   */
> 
>   call usual code since cpufreq is not going to preempt you.
> 
>   if (!is_atomic())
> 	up_read(&freq_sem);
> }

Well, most delays are very short, so...

What about... we decide that cpufreq interruption or switch to
different cpu takes 100usec minimum, and only try to do complex magic
for delays >100usec? Hopefully there's minimum of those :-).

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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