linux-kernel - Re: [RFC -tip 0/4] x86: reduce fixup of uaccess

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Date:	Tue, 6 Jan 2009 11:09:06 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC -tip 0/4] x86: reduce fixup of uaccess


* Hiroshi Shimamoto <h-shimamoto@...jp.nec.com> wrote:

> This is my second try to reduce fixup code size for exceptions of uaccess.
> 
> This patch series reduces fixup code for exceptions of uaccess in signal.
> 
> I gave up to make direct jump to end of function when an exception occurs.
> However, I thought fixup code could be reduced. The concept is that to add
> uaccess_err in thread_info and set it to -EFAULT on exception, finally check
> this value on the last of function.
> 
> Is this good to reduce code size?
> 
> The code size reductions are below;
> $ size *signal*.o.*
>    text	   data	    bss	    dec	    hex	filename
>    4741	      0	      0	   4741	   1285	ia32_signal.o.new
>    6006	      0	      0	   6006	   1776	ia32_signal.o.old
>    3577	      0	      0	   3577	    df9	signal.o.new
>    4540	      0	      0	   4540	   11bc	signal.o.old
>    3855	      0	      0	   3855	    f0f	signal32.o.new
>    4876	      0	      0	   4876	   130c	signal32.o.old

looks very nice! Since kernel execution is i-cache-cold in the typical 
case, this will probably transform into a performance improvement as well.

	Ingo
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