linux-kernel - Re: [PATCH 0/5] sched: Make CONFIG_SCHED

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Message-ID: <83c3bd7f-3ff9-4d3c-ab3e-981b73b95141@linux.ibm.com>
Date: Wed, 19 Mar 2025 18:18:40 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org
Cc: Dietmar Eggemann <dietmar.eggemann@....com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Valentin Schneider <vschneid@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>, Mel Gorman <mgorman@...e.de>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH 0/5] sched: Make CONFIG_SCHED_DEBUG features unconditional



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


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