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    SubjectRe: [patch 1/3] move WARN_ON() out of line
    On Thu, Jan 03, 2008 at 01:56:58AM +0100, Arjan van de Ven wrote:
    > Subject: move WARN_ON() out of line
    > From: Arjan van de Ven <arjan@linux.intel.com>
    > CC: Ingo Molnar <mingo@elte.hu>
    > CC: Andrew Morton <akpm@linux-foundation.org>
    >
    > A quick grep shows that there are currently 1145 instances of WARN_ON
    > in the kernel. Currently, WARN_ON is pretty much entirely inlined,
    > which makes it hard to enhance it without growing the size of the kernel
    > (and getting Andrew unhappy).
    >
    > This patch moves WARN_ON() out of line entirely. I've considered keeping
    > the test inline and moving only the slowpath out of line, but I decided
    > against that: an out of line test reduces the pressure on the CPUs
    > branch predictor logic and gives smaller code, while a function call
    > to a fixed location is quite fast. Likewise I've considered doing something
    > similar to BUG() (eg use a trapping instruction) but that's not really
    > better (it needs the test inline again and recovering from an invalid
    > instruction isn't quite fun).

    Hi Arjan,

    I've got a couple of patches in -mm at the moment that introduces __WARN()
    and uses that (and lets architectures override __WARN, since for example
    powerpc does use trapping instructions similarly to BUG()).

    The two patches in question are:

    bugh-remove-have_arch_bug--have_arch_warn.patch
    powerpc-switch-to-generic-warn_on-bug_on.patch

    Care to do this incrementally on top of that instead? I.e. call
    do_warn_on() from the asm-generic/bug.h __WARN() instead.


    -Olof



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