[LITMUS^RT] CONFIG_HZ and event driven schedulers

[Björn Brandenburg]

On 17.03.2013, at 18:33, Glenn Elliott <gelliott at cs.unc.edu> wrote:

> Out of curiosity, I have a simple question about the proper setting for CONFIG_HZ (Linux's tick rate).
> 
> If we presume the following:
> * the scheduler is event-driven (all of Litmus's schedulers but pfair)
> * we do not use quantum budget enforcement
> * hrtimers are supported
> 
> is there a benefit to setting CONFIG_HZ=1000?  Couldn't we set CONFIG_HZ=100 without increasing latency of real-time scheduling?  We would also benefit from reduced tick overheads.

Yes, that is correct. HZ is entirely irrelevant for event-driven plugins. It only affects Pfair and tick-based budget enforcement. Precise budget enforcement is also hrtimer-driven and hence not affected by HZ, either. So if you know your kernel will not run the pfair plugin, you can pick whatever value you like.

- Björn