Re: [PATCH 0/5] sched: Make CONFIG_SCHED_DEBUG features unconditional

[Shrikanth Hegde]

On 3/20/25 02:44, Ingo Molnar wrote:
> * Shrikanth Hegde <sshegde@xxxxxxxxxxxxx> wrote:
>
> > On 3/17/25 16:12, Ingo Molnar wrote:
> > > For more than a decade, CONFIG_SCHED_DEBUG=y has been enabled
> > > in all the major Linux distributions:
> > >
> > >      /boot/config-6.11.0-19-generic:CONFIG_SCHED_DEBUG=y
> > >
> > > The reason is that while originally CONFIG_SCHED_DEBUG started
> > > out as a debugging feature, over the years (decades ...) it has
> > > grown various bits of statistics, instrumentation and
> > > control knobs that are useful for sysadmin and general software
> > > development purposes as well.
> >
> > A tunable like base_slice which is the only tunable available for EEVDF is under the debug.
> > So an option is to get rid of CONFIG_SCHED_DEBUG and make it available to all.
> >
> > We had seen performance regression when domains folder was built with cpu hotplug.
> > Later that was moved iff verbose was enabled. Maybe something like that can be done
> > if something is hurting performance.
> >
> > > But within the kernel we still pretend that there's a choice,
> > > and sometimes code that is seemingly 'debug only' creates overhead
> > > that should be optimized in reality.
> > >
> > > So make it all official and make CONFIG_SCHED_DEBUG unconditional.
> > > This gets rid of a large amount of #ifdefs, so good riddance ...
> >
> > There are some references in selftest like these, maybe remove them as well?
> >
> > tools/testing/selftests/sched_ext/config:CONFIG_SCHED_DEBUG=y
> > tools/testing/selftests/sched/config:CONFIG_SCHED_DEBUG=y
> > tools/testing/selftests/wireguard/qemu/debug.config:CONFIG_SCHED_DEBUG=y
>
> Indeed - fixed.
>
> I left out all the defconfigs from the patches, because there's a lot
> of them (~79 reference CONFIG_SCHED_DEBUG ...) and they get refreshed
> naturally in any case.
>
> > Also ran unixbench and hackbench on 80 CPU system (1NUMA) with and
> > without CONFIG_SCHED_DEBUG. hackbench numbers are almost the same.
> >
> > for unixbench, process creation/Context Switching show 1-2%
> > improvement with CONFIG_SCHED_DEBUG=n
>
> Thank you for the testing! I'll add:
>
>    Tested-by: Shrikanth Hegde <sshegde@xxxxxxxxxxxxx>
>
> to the series if you don't mind.

It was minimal testing. If that suffices i am okay with the tag.

> And irrespectively of this series we should probably look at that 1-2%
> overhead in unixbench context switching overhead, maybe there's a few
> low hanging fruits in the debug code.
>
> 	Ingo

ok. Let me see perf record and see what shows up.