Re: High resolution timers and BH processing on -RT

Ingo Molnar
2005-01-28T04:43:20Z

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

> Some numbers to make this more transparent.
>
> Machine: PIII Celeron 333MHz
> RT - T0: 1ms cyclic
> RT - T1: 2ms cyclic
> ....
>
> Load average is ~4.0 for all tests. The numbers are maximum deviation
> from the timeline in microseconds. Test time was ~60 minutes for each
> szenario.
>
> Running all timers in high resolution mode (ksoftirqd) results in:
> [T0 Prio: 60] 2123
> [T1 Prio: 59] 2556
> [T2 Prio: 58] 2882
> [T3 Prio: 57] 2993
> [T4 Prio: 56] 2888
>
> Running all timers in high resolution mode (seperated timer softirqd
> PRIO=70) results in:
> [T0 Prio: 60] 423
> [T1 Prio: 59] 372
> [T2 Prio: 58] 756
> [T3 Prio: 57] 802
> [T4 Prio: 56] 1208

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?).

Ingo