linux-kernel - Re: [PATCH] sparc, exec: remove redundant addr

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Date:	Sun, 12 Jun 2011 00:44:15 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	David Miller <davem@...emloft.net>
Cc:	minipli@...glemail.com, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, sparclinux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sparc, exec: remove redundant addr_limit assignment

On Sat, Jun 11, 2011 at 04:08:42PM -0700, David Miller wrote:
> From: Mathias Krause <minipli@...glemail.com>
> Date: Fri, 10 Jun 2011 15:10:53 +0200
> 
> > The address limit is already set in flush_old_exec() so this
> > assignment of USER_DS is redundant.
> > 
> > Signed-off-by: Mathias Krause <minipli@...glemail.com>
>  ...
> > @@ -368,9 +368,6 @@ void flush_thread(void)
> >  
> >  	/* Clear FPU register state. */
> >  	t->fpsaved[0] = 0;
> > -	
> > -	if (get_thread_current_ds() != ASI_AIUS)
> > -		set_fs(USER_DS);
> >  }
> 
> Yeah but now you're doing it unconditionally, the guard is here
> because the %asi register write which set_fs() does is extremely
> expensive on sparc64 and %99.99999 of the time we can avoid it.

OTOH, get_thread_current_ds() is cheap and moving that into set_fs()
itself wouldn't be particulary bad idea...
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