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

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Message-Id: <200802211736.26719.ak@suse.de>
Date:	Thu, 21 Feb 2008 17:36:25 +0100
From:	Andi Kleen <ak@...e.de>
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,
	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

On Thursday 21 February 2008 16:27:22 Gregory Haskins wrote:

> @@ -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()))

I have my doubts that gcc will honor unlikelies that don't affect
the complete condition of an if.

Also conditions guarding returns are by default predicted unlikely
anyways AFAIK. 

The patch is likely a nop.

-Andi
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