Re: [RFC] frandom - fast random generator module

[Andreas Dilger]

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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