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    SubjectRe: [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U8

    * Christoph Hellwig <hch@infradead.org> wrote:

    > > yes, it is valid and perfectly fine code, but i'm trying to separate out
    > > the simple 'mutex' functionality (99% of the semaphore users are just
    > > that) and implement a 'counted semaphore' separately. This removes a
    > > number of implementational constraints from mutexes.
    >
    > So leave the good old struct semaphore alone and introduce a mutex_t..

    with nearly 1000 'struct semaphore' references in the kernel and 980 of
    them being simple mutex use this is rather impractical. So i instead
    went for safely detecting the 20 non-mutex uses and converting those
    places. (Btw., 90% of those 20 cases can be detected safely at
    compile-time (and link-time) by removing DECLARE_MUTEX_LOCKED and making
    sema_init() a macro that only allows constant values of 0 and 1 and
    produces a link error for other cases.)

    this work is still incomplete so i'm not arguing for upstream inclusion.

    (But while we did this a couple of places did turn out to use semaphores
    for completion which is inefficient - we converted those to completions
    and are contributing those changes to mainline. But this issue is
    totally orthogonal to the issue of counted semaphores.)

    Ingo
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