linux-kernel - Re: [PATCH 5/5] remove the extra call to try_to_take

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Message-ID: <Pine.LNX.4.58.0805232301080.12686@gandalf.stny.rr.com>
Date:	Fri, 23 May 2008 23:02:24 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Gregory Haskins <ghaskins@...ell.com>
cc:	mingo@...e.hu, tglx@...utronix.de, linux-rt-users@...r.kernel.org,
	linux-kernel@...r.kernel.org, sdietrich@...ell.com,
	pmorreale@...ell.com, mkohari@...ell.com
Subject: Re: [PATCH 5/5] remove the extra call to try_to_take_lock


On Tue, 20 May 2008, Gregory Haskins wrote:

> From: Peter W. Morreale <pmorreale@...ell.com>
>
> Remove the redundant attempt to get the lock.  While it is true that the
> exit path with this patch adds an un-necessary xchg (in the event the
> lock is granted without further traversal in the loop) experimentation
> shows that we almost never encounter this situation.
>
> Signed-off-by: Peter W. Morreale <pmorreale@...ell.com>
> Signed-off-by: Gregory Haskins <ghaskins@...ell.com>
> ---
>
>  kernel/rtmutex.c |    6 ------
>  1 files changed, 0 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
> index ec1f7d4..1da7813 100644
> --- a/kernel/rtmutex.c
> +++ b/kernel/rtmutex.c
> @@ -785,12 +785,6 @@ rt_spin_lock_slowlock(struct rt_mutex *lock)
>  	spin_lock_irqsave(&lock->wait_lock, flags);
>  	init_lists(lock);
>
> -	/* Try to acquire the lock again: */
> -	if (do_try_to_take_rt_mutex(lock, STEAL_LATERAL)) {
> -		spin_unlock_irqrestore(&lock->wait_lock, flags);
> -		return;
> -	}
> -

This would suggested that lock stealing doesn't happen. On lock stealing,
this is the condition that is triggered and we have a nice quick exit.

-- Steve



>  	BUG_ON(rt_mutex_owner(lock) == current);
>
>  	/*
>
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