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    SubjectRe: [RFC] frandom - fast random generator module
    On Oct 16, 2003  12:45 -0500, Matt Mackall wrote:
    > On Thu, Oct 16, 2003 at 10:20:20AM -0600, Andreas Dilger wrote:
    > > For Lustre we need a low-cost RNG for generating opaque 64-bit handles in
    > > the kernel. The use of get_random_bytes() showed up near the top of
    > > our profiles and we had to invent our own low-cost crappy PRNG instead (it's
    > > good enough for the time being, but when we start working on real security
    > > it won't be enough).
    >
    > Is this SMP? If so, how many processors? I wonder if you might be
    > running into some lock contention in the pool entropy transfer -
    > there's a lock held while mixing new samples into a given pool that
    > could potentially be a hit.

    It was a 2-way SMP system. We use the RNG a fair amount (enough to know
    that 2 CPUs can race and return the same value from get_random_bytes() ;-)
    so we had to put a spinlock around our calls to that. Even so, oprofile
    showed extract_entropy() and SHATransform() near the top of CPU users.

    Cheers, Andreas
    --
    Andreas Dilger
    http://sourceforge.net/projects/ext2resize/
    http://www-mddsp.enel.ucalgary.ca/People/adilger/

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