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    SubjectRe: [PATCH] Use uname not sysctl to get the kernel revision
    On Thu, 2006-07-13 at 00:07 +0100, Alan Cox wrote:
    > Ar Mer, 2006-07-12 am 16:26 -0600, ysgrifennodd Eric W. Biederman:
    > > If the lock is not short lived then the release is like to be a long
    > > ways off. If the lock is not highly contended then you are not likely
    > > to hit the window when someone else as the contended lock.
    > >
    > > How frequent are highly contended short lived locks in user space?
    > I'm not sure it matters.
    > If you want to do the job right then do this
    > - Stick an indicator of how much else wants to run on this CPU in the
    > vsyscall page or similar location

    Except that "this cpu" doesn't really mean anything in userspace, and
    while I think Andi has some tricks to get some sort of CPU number to
    userspace (though it's really only valid during the execution of the
    instruction that reads it :) I haven't yet found an equivalent for
    powerpc (and possibly other architectures will have the same problem).

    > In your locks you can now do
    > while(try_and_grab_lock() == FAILED) {
    > if (kernelpage->waiting > 0)
    > sys_somelockwaitthing()
    > }
    > Furthermore the kernel can be intelligent about the waiting indicator
    > for power or other global scheduling reasons
    > [Disclaimer: There is a patent issue around this technique but its not
    > one that will impact GPL code as permissions are given for GPL use.]
    > Alan

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