Date: Tue, 16 Jun 2009 12:15:20 -0600 From: RB <aoz.syn@...il.com> To: john-users@...ts.openwall.com Subject: Re: MPI John (was: Re: GI John) On Tue, Jun 16, 2009 at 10:50, Minga Minga <mingakore@...il.com> wrote: > The main questions I have are : > > Is MPI+incremental mode faster than --external:Parallel ? > If so, by what percentage? Benefits ? Drawbacks? Single-threaded JtR + MPI is slower than JtR by itself; I don't have the numbers here with me, but IIRC the difference is marginal (if distinct). Hence, the MPI implementation is likely slower than --external:Parallel. What the MPI patch does add is scalability - I personally am willing to sacrifice several percentage points in efficiency for the ability to trivially spread processing over N cores in a large, potentially heterogeneous cluster without having to distribute custom per-node configurations. I've seen indications that it doesn't work well for very large clusters, but the largest I've personally done was 28 cores. > Can I trust MPI to not duplicate effort? I believe so. The modifications to src/inc.c basically cause each MPI thread to leapfrog through the incremental steps. When looking at the log file, a single-threaded run goes through each of the "Trying length X, fixed @Y, character count Z" steps in-order. With the MPI patch, core0 will run "1..N step C", core1 will do "2..N step C", and so on. It's non-optimal and can leave holes in an unbalanced cluster, but it is what it is. > Am I wasting CPU cycles using --external:Parallel for large "incremental" > runs? Doubtful, especially if --external:Parallel fulfills your needs. The Lim MPI patch is far less granular on its split than --external:Parallel, but I'm doubtful the additional per-word modulus adds up to a significant reduction in efficiency. YMMV, and I'm sure someone else here has already run the math. -- To unsubscribe, e-mail john-users-unsubscribe@...ts.openwall.com and reply to the automated confirmation request that will be sent to you.
Powered by blists - more mailing lists
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.