linux-kernel - Re: [PATCH [RT] 11/14] optimize the !printk fastpath through the lock acquisition

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Message-ID: <20080222191837.GE6060@ucw.cz>
Date:	Fri, 22 Feb 2008 20:18:37 +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, gregkh@...e.de, sdietrich@...ell.com,
	pmorreale@...ell.com, mkohari@...ell.com
Subject: Re: [PATCH [RT] 11/14] optimize the !printk fastpath through the lock acquisition

Hi!

> Decorate the printk path with an "unlikely()"
> 
> Signed-off-by: Gregory Haskins <ghaskins@...ell.com>
> ---
> 
>  kernel/rtmutex.c |    8 ++++----
>  1 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
> index 122f143..ebdaa17 100644
> --- a/kernel/rtmutex.c
> +++ b/kernel/rtmutex.c
> @@ -660,12 +660,12 @@ rt_spin_lock_fastlock(struct rt_mutex *lock,
>  		void fastcall (*slowfn)(struct rt_mutex *lock))
>  {
>  	/* Temporary HACK! */
> -	if (!current->in_printk)
> -		might_sleep();
> -	else if (in_atomic() || irqs_disabled())
> +	if (unlikely(current->in_printk) && (in_atomic() || irqs_disabled()))
>  		/* don't grab locks for printk in atomic */
>  		return;
>  
> +	might_sleep();

I think you changed the code here... you call might_sleep() in
different cases afaict.

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