Date: Thu, 4 Jun 2015 20:13:20 +0200 From: Agnieszka Bielec <bielecagnieszka8@...il.com> To: john-dev@...ts.openwall.com Subject: Re: PHC: Lyra2 on CPU 2015-06-02 21:34 GMT+02:00 Solar Designer <solar@...nwall.com>: > On Tue, Jun 02, 2015 at 07:26:52PM +0200, Agnieszka Bielec wrote: >> >> I think that method b) is slower because we are using synchronization >> >> many times and we have barriers for all omp threads. >> > >> > Maybe. You can test this hypothesis by benchmarking at higher cost >> > settings and thus at lower c/s rates. At lower c/s rates, the >> > synchronization overhead becomes relatively lower. >> >> I choose only the biggest noticed speeds for tests: >> ; 8896/9144 >> ~0.97287839020122484689 >> ; 2312/2368 >> ~0.97635135135135135135 > > Can you explain these numbers? I guess these are for two code versions > and two cost settings (that differ by a factor of 4), and you show that > the overhead has stayed the same. Correct? Yet I'd like more specifics > on what you benchmarked here. right: version c) left: version b) up: cost=8,8 down: cost=16,16 overhead isn't the same >> > If confirmed, a way to reduce the overhead at higher c/s rates as well >> > would be via computing larger batches of hashes per parallel for loop. >> > This is what we normally call OMP_SCALE, but possibly applied at a >> > slightly lower level in this case. >> >> lyra2 hash uses barriers in one hash computation so I'm not sure, >> maybe I don't understand your point > > We have multiple hashes to compute, so even if one instance of Lyra2 has > barriers within it we can increase the amount of work done between > barriers by bringing our higher-level parallelism (multiple candidate > passwords) down to that level (to inside of Lyra2 implementation). but don't we need more memory to do this? >> > While we're at it, have you moved the memory (de)allocation out of the >> > cracking loop? And have you done it for POMELO too, as we had >> > discussed - perhaps reusing the allocators from yescrypt? I don't >> > recall you reporting on this, so perhaps this task slipped through the >> > cracks? If so, can you please (re-)add it to your priorities? I implented for lyra b) and c), a) is the worst and I won't be working on a)
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