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    SubjectRe: [patch] SMP alternatives
    On 11/23/05, Daniel Jacobowitz <> wrote:
    > Those are the wrong ways of doing this in userspace. There are right
    > ways. For instance, tag the binary at link time "single-threaded".

    This works and the system is designed this way. But it's unlikely
    that any distribution will ship code like this since the maintenance
    is to problematic.

    > Glibc does not do this to the best of my knowledge. It does select
    > different code paths in various places based on the presence of
    > multiple threads, but that's for cancellation, not for locking.

    Wrong. Linus is right, we jump over lock prefix. After a lot of
    benchmarking I found this to be the fastest was and the Intel people
    seemed to agree.

    > This is also a trivially solvable problem in userspace; you make the
    > dynamic linker enforce consistency of the tags.

    This would require that potentially every single DSO is duplicated as
    threaded and non-threaded. If you like this you might as well enter
    the horror world of BSD with their libc_r. This will never fly, the
    support costs are too high.

    > The number of userspace libraries that use atomic operations is, in
    > practice, quite small.

    It really not and the number using them is growing.

    ➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖
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