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    SubjectRe: Intel P6 vs P7 system call performance

    On Thu, 19 Dec 2002, Jamie Lokier wrote:
    > Linus Torvalds wrote:
    > > For _zero_ gain. The jump to the library address has to be indirect
    > > anyway, and glibc has several places to put the information without any
    > > mmap's or anything like that.
    >
    > This is not true, (but your overall point is still correct).

    Go back and read the postings by Uli.

    Uli's suggested glibc approach is to just put the magis system call
    address (which glibc gets from the AT_SYSINFO elf aux table entry) into
    the per-thread TLS area, which is alway spointed to by %gs anyway.

    THIS WORKS WITH ALL DSO'S WITHOUT ANY GAMES, ANY MMAP'S, ANY RELINKING, OR
    ANY EXTRA WORK AT ALL!

    The system call entry becomes a simple

    call *%gs:constant-offset

    Not mmap. No magic system calls. No relinking. Not _nothing_. One
    instruction, that's it.

    See for example Uli's posting in this thread from the day before
    yesterday, message ID <3DFF6D4B.3060107@redhat.com>. So please stop
    arguing about any extra work, because none is needed.

    Linus

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