Re: High resolution timers and BH processing on -RT

Ingo Molnar
2005-01-28T08:24:52Z

* Thomas Gleixner <tglx@linutronix.de> wrote:

> > is this due to algorithmic/PIT-programming overhead, or due to the noise
> > introduced by other, non-hard-RT timers? I'd guess the later from the
> > looks of it, but did your test introduce such noise (via networking and
> > application workloads?).
>
> Right, it's due to noise by non-RT timers, which I enforced by adding
> networking and applications.
>
> This adds random timer expires and admittedly the PIT reprogramming
> overhead is adding portions of that noise.

i havent seen your latest code - what is the basic data-structure? The
stock kernel has arrays of timers with increasing granularity and a
cascade mechanism to move timers down the arrays as they slowly expire -
but with a high-resolution API (1 usec accuracy?) how does the basic
data structure look like?

Is the "noise" due to timers expiring "at once" - but isnt it unlikely
for 'normal' timers to expire in exactly the same usec as the real
high-resolution one?

or is it that we have a 'group' of normal timers expiring, which, if
they happen to occur _just_ prior a HRT event will generate a larger
delay?

Ingo