Date: Wed, 16 May 2012 18:26:46 +0400 From: Solar Designer <solar@...nwall.com> To: john-dev@...ts.openwall.com Subject: OpenCL vs. CUDA CPU usage Hi, This is just an observation: somehow with CUDA we're fully wasting an entire CPU core per GPU, whereas with OpenCL we're only using some CPU time on one core: user@...l:~$ ps axuw | fgrep -w john user 14325 9.2 0.8 21345708 72932 pts/3 SNl+ 17:52 2:40 ./john /home/user/john/contest-2011/hashes-all.txt-3.phpass -i -fo=phpass-opencl -pla=1 user 14702 100 0.4 21154568 38384 pts/4 RNl+ 18:10 10:43 ./john /home/user/john/contest-2011/hashes-all.txt-3.phpass -i -fo=phpass-cuda -se=n Notice how the OpenCL run (using the 7970 card) consumes only 9.2% CPU, whereas the CUDA run (using the 570) consumes 100% (I guess mostly wasted on active waits for the GPU). I wonder if there's a tunable setting for CUDA to make it wait passively (so that the CPU would stay cooler or we could use this CPU core by another instance of John). I also wonder if we'd see the same CPU wastage with OpenCL on the 570. I can easily try that next, indeed. Alexander
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