linux-kernel - Re: [(RT RFC) PATCH v2 2/9] sysctl for runtime-control of lateral mutex stealing

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Message-ID: <20080225215335.GE2659@elf.ucw.cz>
Date:	Mon, 25 Feb 2008 22:53:35 +0100
From:	Pavel Machek <pavel@....cz>
To:	Gregory Haskins <ghaskins@...ell.com>
Cc:	mingo@...e.hu, a.p.zijlstra@...llo.nl, tglx@...utronix.de,
	rostedt@...dmis.org, linux-rt-users@...r.kernel.org,
	linux-kernel@...r.kernel.org, bill.huey@...il.com,
	kevin@...man.org, cminyard@...sta.com, dsingleton@...sta.com,
	dwalker@...sta.com, npiggin@...e.de, dsaxena@...xity.net,
	ak@...e.de, acme@...hat.com, gregkh@...e.de, sdietrich@...ell.com,
	pmorreale@...ell.com, mkohari@...ell.com
Subject: Re: [(RT RFC) PATCH v2 2/9] sysctl for runtime-control of lateral
	mutex stealing

Hi!

> From: Sven-Thorsten Dietrich <sdietrich@...e.de>
> 
> Add /proc/sys/kernel/lateral_steal, to allow switching on and off
> equal-priority mutex stealing between threads.
> 
> Signed-off-by: Sven-Thorsten Dietrich <sdietrich@...e.de>
> ---
> 
>  kernel/rtmutex.c |    7 ++++++-
>  kernel/sysctl.c  |   14 ++++++++++++++
>  2 files changed, 20 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
> index 6624c66..cd39c26 100644
> --- a/kernel/rtmutex.c
> +++ b/kernel/rtmutex.c
> @@ -18,6 +18,10 @@
>  
>  #include "rtmutex_common.h"
>  
> +#ifdef CONFIG_RTLOCK_LATERAL_STEAL
> +int rtmutex_lateral_steal __read_mostly = 1;
> +#endif
> +

Ugly..


>  /*
>   * lock->owner state tracking:
>   *
> @@ -321,7 +325,8 @@ static inline int lock_is_stealable(struct task_struct *pendowner, int unfair)
>  	if (current->prio > pendowner->prio)
>  		return 0;
>  
> -	if (!unfair && (current->prio == pendowner->prio))
> +	if (unlikely(current->prio == pendowner->prio) &&
> +	   !(unfair && rtmutex_lateral_steal))
>  #endif

But this is even worse, you are creating #ifdef maze here. Can you
simply #define rtmutex_lateral_steal 0 in !CONFIG_RTLOCK_LATERAL_STEAL
and let the optimizer fix this?


> index c913d48..c24c53d 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -175,6 +175,10 @@ extern struct ctl_table inotify_table[];
>  int sysctl_legacy_va_layout;
>  #endif
>  
> +#ifdef CONFIG_RTLOCK_LATERAL_STEAL
> +extern int rtmutex_lateral_steal;
> +#endif
> +

Try checkpatch.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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