Re: HZ > 100 overhead

[Benno Senoner <sbenno@gardena.net>]

On Wed, 27 Oct 1999, Paul Barton-Davis wrote:
> >> >Wouldn't you say that an HZ > 100 kernel is the cleanest solution?
> >> 
> >> its the cleanest, but not the best. HZ = 1000 adds about 8% overhead
> >> to IRQ processing *all the time*.
> >
> >Are you *sure* about this?  I seem to remember there was some debate
> >about that figure on linux-kernel.
> 
> Ed Hall measured it, and my overall impression of Ed is that I'd trust
> him to do this correctly. what did the l-k folks think ?

It depends on your box, a P133 might suffer much more than a PII400.
On a PII400 the performance his is very little IMHO (no actual numbers)

But we can't assume that HZ\x1000 for our multimedia apps.
Therefore my proposal is the following:
(similar to Eric's proposed rtcd)
In our upcoming multimedia API we will run the audio daemon
not only for providing PCM/MIDI services but precise timers too.
This could be implemented by choosing the most efficient method
at the moment:
that means: if you are runnnig with 1ms audio buffer sizes,
instead of firing up the RTC device, use the soundcard's timer
(combined with RDTSC) , to wakeup your clients.

comments ?

Benno.