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    SubjectRe: [PATCH 3/3] kmemtrace: Use tracepoints instead of markers.
    * Eduard - Gabriel Munteanu (eduard.munteanu@linux360.ro) wrote:
    > On Mon, Jan 05, 2009 at 11:05:34AM -0500, Mathieu Desnoyers wrote:
    > > Hopefully it does, especially when there are no side-effects. Can you
    > > also try with -Os ?
    > >
    > > Mathieu
    >
    > Here's the disassembled code when using -Os. It seems it's optimised, as
    > with -O2. My GCC's version is 4.3.2 (Gentoo Linux).
    >
    > If you want to test yourself, the output was generated with 'objdump -d
    > -S -a'.
    >
    > What do you think?
    >
    > static void print_that(unsigned long num)
    > {
    > printf("input << 5 == %lu\n", num);
    > 40062d: 48 c1 e6 05 shl $0x5,%rsi
    > 400631: bf 5e 07 40 00 mov $0x40075e,%edi
    > 400636: 31 c0 xor %eax,%eax
    > 400638: e8 6b fe ff ff callq 4004a8 <printf@plt>
    > sscanf(argv[2], "%lu", &in);
    >
    > call_do_something(in);
    >
    > return 0;
    > }
    > 40063d: 5a pop %rdx
    > 40063e: 59 pop %rcx
    > 40063f: 31 c0 xor %eax,%eax
    > 400641: 5b pop %rbx
    > 400642: c3 retq
    >
    >
    > Eduard
    >

    It looks good. Although I wonder if gcc will still optimize this in more
    complicated functions. Just to be 100% sure, I would recommend testing
    it in larger functions like schedule() in the kernel tree. But so far it
    looks like it does not hurt much to leave a small supplementary operation
    in the unlikely() branch.

    Mathieu

    --
    Mathieu Desnoyers
    OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68


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