linux-kernel - Re: [RFC][PATCH] signal: replace !likely with unlikely!

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Message-ID: <20140911191830.GA31511@roeck-us.net>
Date:	Thu, 11 Sep 2014 12:18:30 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	roy.qing.li@...il.com
Cc:	linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk,
	fabf@...net.be, jkosina@...e.cz, paulmck@...ux.vnet.ibm.com,
	richard@....at, oleg@...hat.com, akpm@...ux-foundation.org
Subject: Re: [RFC][PATCH] signal: replace !likely with unlikely!

On Thu, Sep 11, 2014 at 08:48:16AM +0800, roy.qing.li@...il.com wrote:
> From: Li RongQing <roy.qing.li@...il.com> 
> 
> !likely() is hard to be understood, and I do not know if compiler can
> optimise this condition, but unlikely(!()) is clear
> 
> Signed-off-by: Li RongQing <roy.qing.li@...il.com>
> ---
>  kernel/signal.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/signal.c b/kernel/signal.c
> index 8f0876f..6156cfa 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -1571,7 +1571,7 @@ int send_sigqueue(struct sigqueue *q, struct task_struct *t, int group)
>  	BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));
>  
>  	ret = -1;
> -	if (!likely(lock_task_sighand(t, &flags)))
> +	if (unlikely(!lock_task_sighand(t, &flags)))

I wonder if you tested this code. Seems to be unlikely (punt not intended).

Guenter

>  		goto ret;
>  
>  	ret = 1; /* the signal is ignored */
> -- 
> 1.7.10.4
> 
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