Date: Wed, 19 Aug 2015 08:51:52 +0200 From: magnum <john.magnum@...hmail.com> To: john-dev@...ts.openwall.com Subject: Re: Long duration formats' many-salts figure incorrect in short benchmarks On 2015-08-18 23:41, Solar Designer wrote: > On Tue, Aug 18, 2015 at 11:31:52PM +0200, magnum wrote: >> [...] the benchmark timer ends before we even get to try the second >> salt even once! > [...] >> Longer runs show better figures (within limits). This problem is with >> "your code", but it never surfaces in non-Jumbo. I'm not sure whether to >> fix this, or how. Should we simply ensure the while loop runs long >> enough for both salts to be tested at least once? Maybe that would end >> up showing a mere 2x boost in this case? Should we ensure the loop does >> all BENCHMARK_MANY virtual salts? But that would likely end up in some >> GPU formats benchmarking for hours... > > Yes, there's this problem with no obviously correct solution. Testing > every salt at least once makes sense to me because we've already done so > during the self-test. This might increase the test+benchmark time by > more than a factor of 2, though, since the self-tests run up to a lower > crypt_all() count argument for most of its invocations. But it > shouldn't be worse than 4x overall. What's worse is that, as you > correctly point out, this might not achieve the full BENCHMARK_MANY > speed, requiring the user to manually increase the benchmark duration to > see that. Perhaps just emit a warning? Something like this (mockup): Benchmarking: 7z-opencl, 7-Zip (512K iterations) [SHA256 OPENCL AES]... (8xOMP) DONE Speed for cost 1 (iteration count) of 524288 Warning: "Many salts" test limited: 1/256 Many salts: 108 c/s real, 12800 c/s virtual Only one salt: 108 c/s real, 12800 c/s virtual Not sure what the actual message should be. The one in this example would indicate we only tried one virtual salt out of 256. magnum
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