Date: Thu, 15 Mar 2012 23:24:07 +0200 From: Milen Rangelov <gat3way@...il.com> To: john-dev@...ts.openwall.com Subject: Re: AMD Bulldozer and XOP Hello :) > It got plenty of buggy code already, adding some more wouldn't hurt. ;-) > Seriously, though, I think many contributions are useful as PoCs - then > other contributors to the project may re-code things in a cleaner way. I can help with some kernels. In fact, JtR is very inspiring project. I like to look at how people solved similar problems often in different ways. > I'm sorry, that comment of mine was wrong and misleading. For a moment > I confused VEX-encoding vs. not with XMM vs. YMM registers. Indeed, > VPCMOV exists for XMM registers as well, and in fact this is what JtR > normally uses in -xop builds (except in 32-bit x86 builds, where it > tries to use 256-bit AVX and XOP to compensate for the low register > count, which in practice turned out to be beneficial on Sandy Bridge, > but not on Bulldozer - so I am going to stop doing that for -xop). > > So 256-bit XOP is slower than 128-bit one? This reminds me of SSE2 and some old Pentium 4 CPUs :) > Yeah, I was surprised to hear you got into the CPU stuff at all - I > thought you were a GPU guy. ;-) > > Not exactly. I like GPGPU stuff though, it's still easy and predictable and very challenging at times. It's also much more straightforward - you get what you see. When coding CPU stuff with performance in mind, there are just so many factors and the x86 architecture itself is a monster :) > Like I said above, the 256-bit bitwise ops are currently slow. On Sandy > Bridge, they deliver about the same per-bit speed that the 128-bit ones > do, and on Bulldozer they appear to be slower. Things should change > with future CPUs, though - especially with those supporting AVX2 (which > officially gives us 256-bit integer vectors). > That's bad. I expected some decent speedup by using 256-bit vectors. Looks like I should wait until Haswell (or whatever the first AVX2 chip is) comes out... Regards Content of type "text/html" skipped
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