Re: Observation on NOHZ_FULL

[Uladzislau Rezki <urezki@gmail.com>]

> > 
> > I repeated some tests in a more isolated environment and posted the
> > results here:
> > https://discourse.ubuntu.com/t/enable-low-latency-features-in-the-generic-ubuntu-kernel-for-24-04/42255
> > 
> > Highlights:
> > 
> >  - stress-ng --matrix seems quite unpredictable to be used a benchmarks
> >    in this scenario (the bogo-ops/s are very susceptible to any kind of
> >    interference, so even if in the long runs NO_HZ_FULL still seems to
> >    provide some benefits looking at the average, we also need to
> >    consider that there might be a significant error in the measurements,
> >    standard deviation was pretty high)
> > 
> >  - fio doing short writes (in page cache) seems to perform like 2x
> >    better in terms of iops with nohz_full, respect to the other cases
> >    and it performs 2x slower with large IO writes (not sure why... need
> >    to investigate more)
> > 
> >  - with lazy RCU enabled hrtimer_interrupt() takes like 2x more to
> >    return, respect to the other cases (is this expected?)
> 
> This last is surprising at first glance, but I could be missing
> something.  Joel, Uladzislau, thoughts?
> 
Could you please share the steps how you run "fio" tests?

--
Uladzislau Rezki