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    SubjectRe: semaphore and mutex in current Linux kernel (3.2.2)

    * Chen, Dennis (SRDC SW) <Dennis1.Chen@amd.com> wrote:

    > Documentation/mutex-design.txt:
    >
    > "- 'struct mutex' is smaller on most architectures: E.g. on x86,
    > 'struct semaphore' is 20 bytes, 'struct mutex' is 16 bytes.
    > A smaller structure size means less RAM footprint, and better
    > CPU-cache utilization."
    > ================================================================
    >
    > Now in my x86-64 32-bit Linux environment, 'struct semaphone'
    > is 16 bytes, 'struct mutex' is 20 bytes. So seems the RAM
    > footprint advantages are not there...

    It got larger due to the adaptive spin-mutex performance
    optimization.

    > For the performance advantages followed, I don't have the
    > ./test-mutex and maybe the testing environment, so haven't the
    > 1st hand data for this item...

    Well, a way to reproduce that would be to find a lock_mutex
    intense workload ('perf top -g', etc.), and then changing back
    the underlying mutex to a semaphore, and measure the performance
    of the two primitives.

    Thanks,

    Ingo


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