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

[Pavel Machek <pavel@ucw.cz>]

Hi!

> From: Sven-Thorsten Dietrich <sdietrich@suse.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@suse.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
-- 
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