linux-kernel - Re: Runtime overhead of PREEMPT

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Message-ID: <c6259a1824e570ddb7aaf114656aa387e028b76d.camel@gmx.de>
Date:   Fri, 20 Oct 2023 16:11:43 +0200
From:   Mike Galbraith <efault@....de>
To:     Emanuele Rocca <ema@...ian.org>
Cc:     linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...e.com>
Subject: Re: Runtime overhead of PREEMPT_DYNAMIC

On Fri, 2023-10-20 at 15:40 +0200, Emanuele Rocca wrote:
> Hi Mike,
>
> Here is the full diff between the kernel configurations I used. The only
> change I made was setting CONFIG_PREEMPT_DYNAMIC=n, everything else was
> a consequence of that AFAICT, but please do let me know if you see
> anything that shouldn't be there.
>
> --- config-6.5.0-0.preempt-dynamic-amd64        2023-10-11 15:30:02.000000000 +0200
> +++ config-6.5.0-0.a.test-amd64 2023-10-11 14:30:02.000000000 +0200
>
> @@ -10597,7 +10596,6 @@
>  # end of Scheduler Debugging
>  
>  # CONFIG_DEBUG_TIMEKEEPING is not set
> -CONFIG_DEBUG_PREEMPT=y
>  
>  #
>  # Lock Debugging (spinlocks, mutexes, etc...)

Seems you had also turned on DEBUG_PREEMPT in the dynamic setup, which
adds some overhead.. but not a metric ton.

	-Mike