Re: [PATCH 1/2] sched/isolation: Add cpu_is_isolated() API

[Marcelo Tosatti]

On Thu, Mar 30, 2023 at 03:28:52PM +0200, Michal Hocko wrote:
> > > Is this a best practice documented anywhere or it just happens to be
> > > the case with workloads you deal with?
> > 
> > Option 2. However Frederic seems interested in matching the exported
> > toggles with the known use-cases classes.
> > 
> > For example, for this guide:
> > http://www.comfilewiki.co.kr/en/doku.php?id=comfilepi:improving_real-time_performance:index
> > 
> > Using nohz_full= would be a benefit (and its not being currently set,
> > perhaps due to not knowing all the options?).
> > 
> > http://www.comfilewiki.co.kr/en/doku.php?id=comfilepi:improving_real-time_performance:index
> > 
> > 
> > AFAIU the workloads for which disabling nohz_full= is a benefit are those
> > where the switching between nohz full mode and sched tick enabled mode
> > and vice-versa (which involve programming the local timer) happens
> > often and is therefore avoidable? For example switching between 1
> > runnable task and more than 1 runnable task (and vice versa).
> 
> The patch from Frederic is testing for both. You seem to be arguing to
> reduce the test and I still do not understand why. Sure some workloads
> (following the above) will likely use nohz_full= as well but does it
> make sense to build that expectation into the higher level logic? What
> is an actual benefit?

Just thinking of simpler code. Feel free to maintain the patch as-is if
you see fit.