Date: Fri, 26 Mar 2010 07:22:31 +0300 From: Solar Designer <solar@...nwall.com> To: john-users@...ts.openwall.com Subject: Re: bench.c fix for extreme c/s figures On Thu, Mar 25, 2010 at 10:58:03PM +0100, Magnum, P.I. wrote: > Running under MPI, I experienced c/s rollover even from just a couple of > seconds of NT benchmarking. Did you exceed 4G hash computations in just a few seconds? I think you'd need to have a hundred of nodes to achieve that currently - did you really have this many? > The problem was only when benchmarking, not > real cracking. I identified it as due to the sloppy conversion in this > line in benchmark_cps() in bench.c: > > tmp.lo = count; tmp.hi = 0; It was assumed that "count" could be 32-bit anyway (on some builds it is) and that it would be relatively small (which it is on single CPU core runs so far). However, I was using a 64-bit integer variable for some further computation involving multiplication by clk_tck. Then it is once again assumed that the c/s rate for a cipher fits in 32 bits. > Enclosed is the dilettant take I made to make it better (along with some > more scaling, to mega and giga c/s) which was included in fullmpi-5. > This should apply more or less cleanly to standard john too. I am avoiding "long long" in official JtR code so far, so I'd need to implement this differently. Also, div64by32lo() returns a 32-bit value anyway. BTW, I am considering changing math.[ch] to implement 128-bit or maybe even bigger integers. > This fix > works just fine on my gear, but W.A's OSX system (using 64-bit longs and > presumably the same for ARCH_WORD) now reportedly produces figures of > "4294M c/s" for both real and virtual and for all and any formats, > whether fast or not and even when running on just one node. > > I'm willing to admit I am the worst coder on earth but while I recognize > that figure, I don't really see what went wrong? It looks like div64by32lo() detects overflow of its 32-bit return value, which happens when tmp.hi is higher than time. I am puzzled as to why this would be happening on W.A.'s system in all cases, although I haven't reviewed your patch other than bench.c.patch. Alexander
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