Re: Observation on NOHZ_FULL

[Uladzislau Rezki <urezki@gmail.com>]

On Mon, Jan 29, 2024 at 05:47:39PM +0000, Joel Fernandes wrote:
> Hi Guys,
> Something caught my eye in [1] which a colleague pointed me to
>  - CONFIG_HZ=1000 : 14866.05 bogo ops/s
>  - CONFIG_HZ=1000+nohz_full : 18505.52 bogo ops/s
> 
> The test in concern is:
> stress-ng --matrix $(getconf _NPROCESSORS_ONLN) --timeout 5m --metrics-brief
> 
> which is a CPU intensive test.
> 
> Any thoughts on what else can attribute a 30% performance increase
> versus non-nohz_full ? (Confession: No idea if the baseline is
> nohz_idle or no nohz at all). If it is 30%, I may want to evaluate
> nohz_full on some of our limited-CPU devices :)
> 
Timer overhead and its scheduler-callback? If i do not mess something
the NO_HZ_FULL will disable the timer if there is only one task on CPU
so that running task benefits from not being interrupted thus gets more
CPU time.

--
Uladzislau Rezki