linux-kernel - Re: [PATCH] lib/Kconfig.debug: add a comment to PROVE

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Date:   Tue, 9 Oct 2018 18:53:54 +0300
From:   Nikolay Borisov <nborisov@...e.com>
To:     Lukasz Luba <l.luba@...tner.samsung.com>,
        linux-kernel@...r.kernel.org
Cc:     b.zolnierkie@...sung.com, longman@...hat.com, mingo@...hat.com
Subject: Re: [PATCH] lib/Kconfig.debug: add a comment to PROVE_LOCKING impact



On  9.10.2018 18:39, Lukasz Luba wrote:
> This patch add some comment related to performance impact,
> which can be really big (x3 times slower context switch).
> 
> Signed-off-by: Lukasz Luba <l.luba@...tner.samsung.com>

I don't think this brings any value. lockdep is a debugging aid aimed at
developers. A developer should be aware that it has a performance impact
and the classification x3 doesn't really bring anything.
> ---
>  lib/Kconfig.debug | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 4966c4f..9e67a2a3 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1088,6 +1088,9 @@ config PROVE_LOCKING
>  	 the proof of observed correctness is also maintained for an
>  	 arbitrary combination of these separate locking variants.
>  
> +	 This feature enables LOCKDEP which can harm system performance
> +	 even x3 times.
> +
>  	 For more details, see Documentation/locking/lockdep-design.txt.
>  
>  config LOCK_STAT
> @@ -1112,6 +1115,10 @@ config LOCK_STAT
>  	 CONFIG_LOCK_STAT defines "contended" and "acquired" lock events.
>  	 (CONFIG_LOCKDEP defines "acquire" and "release" events.)
>  
> +	 This feature enables LOCKDEP which can harm system performance
> +	 even x3 times.
> +	 For more details, see Documentation/locking/lockdep-design.txt.
> +
>  config DEBUG_RT_MUTEXES
>  	bool "RT Mutex debugging, deadlock detection"
>  	depends on DEBUG_KERNEL && RT_MUTEXES
> @@ -1175,6 +1182,10 @@ config DEBUG_LOCK_ALLOC
>  	 spin_lock_init()/mutex_init()/etc., or whether there is any lock
>  	 held during task exit.
>  
> +	 This feature enables LOCKDEP which can harm system performance
> +	 even x3 times.
> +	 For more details, see Documentation/locking/lockdep-design.txt.
> +
>  config LOCKDEP
>  	bool
>  	depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT
>