Re: [PATCH] common implementation of iterative div/mod

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 08 May 2008 16:16:41 +0100 Jeremy Fitzhardinge <jeremy@goop.org> wrote:

> We have a few instances of the open-coded iterative div/mod loop, used
> when we don't expcet the dividend to be much bigger than the divisor.
> Unfortunately modern gcc's have the tendency to strength "reduce" this
> into a full mod operation, which isn't necessarily any faster, and
> even if it were, doesn't exist if gcc implements it in libgcc.
> 
> The workaround is to put a dummy asm statement in the loop to prevent
> gcc from performing the transformation.
> 
> This patch creates a single implementation of this loop, and uses it
> to replace the open-coded versions I know about.

Believe it or not, this patch causes one of my test machines to fail to
find its disk.

good dmesg: http://userweb.kernel.org/~akpm/dmesg-t61p.txt
bad dmesg: http://userweb.kernel.org/~akpm/dmesg-t61p-dead.txt
config: http://userweb.kernel.org/~akpm/config-t61p.txt