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Date: Thu, 12 Jun 2014 16:46:22 -0400 From: Theodore Ts'o <tytso@....edu> To: George Spelvin <linux@...izon.com> Cc: hpa@...ux.intel.com, linux-kernel@...r.kernel.org, mingo@...nel.org, price@....edu Subject: Re: random: Benchamrking fast_mix2 So I just tried your modified 32-bit mixing function where you the rotation to the middle step instead of the last step. With the usleep(), it doesn't make any difference: # schedtool -R -p 1 -e /tmp/fast_mix2_48 fast_mix: 212 fast_mix2: 400 fast_mix3: 400 fast_mix: 208 fast_mix2: 408 fast_mix3: 388 fast_mix: 208 fast_mix2: 396 fast_mix3: 404 fast_mix: 224 fast_mix2: 408 fast_mix3: 392 fast_mix: 200 fast_mix2: 404 fast_mix3: 404 fast_mix: 208 fast_mix2: 412 fast_mix3: 396 fast_mix: 208 fast_mix2: 392 fast_mix3: 392 fast_mix: 212 fast_mix2: 408 fast_mix3: 388 fast_mix: 200 fast_mix2: 716 fast_mix3: 773 fast_mix: 426 fast_mix2: 717 fast_mix3: 728 without the usleep() I get: 692# schedtool -R -p 1 -e /tmp/fast_mix2_48 fast_mix: 104 fast_mix2: 224 fast_mix3: 176 fast_mix: 56 fast_mix2: 112 fast_mix3: 56 fast_mix: 56 fast_mix2: 64 fast_mix3: 64 fast_mix: 64 fast_mix2: 64 fast_mix3: 48 fast_mix: 56 fast_mix2: 64 fast_mix3: 56 fast_mix: 56 fast_mix2: 64 fast_mix3: 64 fast_mix: 56 fast_mix2: 64 fast_mix3: 64 fast_mix: 56 fast_mix2: 72 fast_mix3: 56 fast_mix: 56 fast_mix2: 64 fast_mix3: 56 fast_mix: 64 fast_mix2: 64 fast_mix3: 56 I'm beginning to suspect that some of the differences between your measurements and mine might be that in addition to having a smaller cache (8M instead of 12M), I suspect there are some other caches, perhaps the uop cache, which are also smaller on the mobile processor, and that is explaining why you are seeing some different results. > > Of course, using wider words works fantastically. > These constants give 76 bits if avalanche after 2 rounds, > essentially full after 3.... And here is my testing using your 64-bit variant: # schedtool -R -p 1 -e /tmp/fast_mix2_49 fast_mix: 294 fast_mix2: 476 fast_mix4: 442 fast_mix: 286 fast_mix2: 1058 fast_mix4: 448 fast_mix: 958 fast_mix2: 460 fast_mix4: 1002 fast_mix: 940 fast_mix2: 1176 fast_mix4: 826 fast_mix: 476 fast_mix2: 840 fast_mix4: 826 fast_mix: 462 fast_mix2: 840 fast_mix4: 826 fast_mix: 462 fast_mix2: 826 fast_mix4: 826 fast_mix: 462 fast_mix2: 826 fast_mix4: 826 fast_mix: 462 fast_mix2: 826 fast_mix4: 826 fast_mix: 462 fast_mix2: 840 fast_mix4: 826 ... and without usleep() 690# schedtool -R -p 1 -e /tmp/fast_mix2_48 fast_mix: 52 fast_mix2: 116 fast_mix4: 96 fast_mix: 32 fast_mix2: 32 fast_mix4: 24 fast_mix: 28 fast_mix2: 36 fast_mix4: 24 fast_mix: 32 fast_mix2: 32 fast_mix4: 24 fast_mix: 32 fast_mix2: 36 fast_mix4: 24 fast_mix: 36 fast_mix2: 32 fast_mix4: 24 fast_mix: 32 fast_mix2: 36 fast_mix4: 28 fast_mix: 28 fast_mix2: 28 fast_mix4: 24 fast_mix: 32 fast_mix2: 36 fast_mix4: 28 fast_mix: 32 fast_mix2: 32 fast_mix4: 24 The bottom line is that what we are primarily measuring here is all different cache effects. And these are going to be quite different on different microarchitectures. That being said, I wouldn't be at all surprised if there are some CPU's where the extract memory dereference to the twist_table[] would definitely hurt, since Intel's amazing cache architecture(tm) is no doubt covering a lot of sins. I wouldn't be at all surprised if some of these new mixing functions would fare much better if we tried benchmarking them on an 32-bit ARM processor, for example.... - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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