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    SubjectRe: [Patch 4/4] Tell GCC 4.1 to move unlikely() code to a separate section
    Andi Kleen wrote:
    > On Monday 27 February 2006 16:31, Arjan van de Ven wrote:
    >> This patch is more controversial I assume; it offers the option
    >> to use the gcc 4.1 option to move unlikely() code to a separate section.
    >> On the con side, this means that longer byte sequences are needed to jump
    >> to this code, on the Pro side it means that the unlikely() code isn't sharing
    >> icache cachelines and tlbs anymore.
    >
    > I don't think this will do anything because the default Makefile
    > still has
    >
    > CFLAGS += -fno-reorder-blocks
    >
    > That was me because it made assembly debugging much easier. I would be willing
    > to reconsider this if you can give me some hard data just from this change:
    > - benchmark changes
    > - .text size increase
    >
    > Also I don't like it being an separate CONFIG options. We already have too many
    > obscure ones. Either it should be on by default or not there at all.

    I think you just made the case for an option, if it does produce
    substantially better code and justify being done, you still would want a
    way to kill it for debugging.

    I'd like to see what it gains in general, and how much it depends on
    processor type and cache size.
    --
    -bill davidsen (davidsen@tmr.com)
    "The secret to procrastination is to put things off until the
    last possible moment - but no longer" -me

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