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    SubjectRe: [PATCH] Linux Kernel Markers 0.14 for 2.6.17
    * Jeremy Fitzhardinge ( wrote:
    > Mathieu Desnoyers wrote:
    > >Hi,
    > >
    > >Constructing on Jeremy Fitzhardinge's comments about gcc optimizations, I
    > >rewrote (once more) the markers mechanism so that the optimized mode does
    > >not
    > >jump between two different inline asm. Instead, the optimized version uses
    > >a
    > >load immediate (in assembly) that will be used by a test to decide of a
    > >branch
    > >(in C).
    > >
    > I should have spelled out my point a bit more. If you've got a flag
    > you're just testing, couldn't you just do:
    > if (__mark_enabled_##name)
    > (*__mark_func)(...);
    > and do without the asms or the section?

    Because a supplementary memory read is added on the critical path with a normal
    flag test. The assembly can provide an immediate value without any need of
    memory read from the data section.

    To change the behavior of the program, I just have to change the immediate value
    in the movb instruction.

    However, the non-optimized generic version does exactly this : it simply tests a
    flag loaded from memory. It can be very useful on embedded systems where the
    code is in read-only memory.



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      Last update: 2006-09-27 00:31    [W:0.028 / U:0.008 seconds]
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