linux-kernel - Re: Runtime overhead of PREEMPT

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Message-ID: <ZTKScoO9kz_LxNMG@ariel>
Date:   Fri, 20 Oct 2023 16:45:06 +0200
From:   Emanuele Rocca <ema@...ian.org>
To:     Mike Galbraith <efault@....de>
Cc:     linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...e.com>
Subject: Re: Runtime overhead of PREEMPT_DYNAMIC

On 2023-10-20 04:34, Mike Galbraith wrote:
> Hm, I don't recall the overhead as being that bad, but thar she blows.
> 
> i7-4790                                       avg         cmdline
> 6.5.8-voluntary 3685.08 3679.93 3704.98   3689.99  1.000
> 6.5.8-dynamic   3571.62 3568.61 3550.55   3563.59   .965
>                 3052.06 3032.74 3019.93   3034.91   .822  +DEBUG_PREEMPT
>                 3651.37 3599.87 3615.18   3622.14   .981  preempt=none
>                 3459.58 3514.09 3539.88   3504.51   .949  preempt=full

Perfect, that's in line with my measurements (~20% overhead). Debian
kernels have CONFIG_DEBUG_PREEMPT=y, it seems wise to set it to 'n'
instead. Thank you.