Author: Vincent Diepeveen
Date: 07:08:42 05/13/02
Go up one level in this thread
On May 12, 2002 at 09:09:11, Jeremiah Penery wrote: >On May 12, 2002 at 07:18:07, Vincent Diepeveen wrote: > >>On May 11, 2002 at 13:14:02, Jeremiah Penery wrote: >> >>>On May 11, 2002 at 09:38:15, Vincent Diepeveen wrote: >>> >>>>For a 64 bits cpu to be interesting for chess they need to do something >>>>no one ever has managed before. >>> >>>And that is...? The Alpha seems pretty nice, as well as POWER4, according to >>>SPECInt numbers (for Crafty). Just because they aren't good for DIEP doesn't >>>mean they can't be good for chess. You don't even use 64-bit variables in DIEP >>>(right?), so why would you expect a 64-bit chip to be any faster for you? >> >>i'm using 'int' so if a compiler rewrites that to 64 bits, then it's >>DIEP is a 64 bits program. > >No it's not. You're going to have half those bits filled with zeros, so it's >irrelevant. No that's not irrelevant. If your 32 bits code must to to a special slow 32 bits part of the cpu (like the IA64 has a few of those) then that's going to slow down the program *a lot*. If it can get compiled into 64 bits code then that's removing *that* disadvantage at least of needing 32 bits execution units. >>a 64 bits cpu is completely different from 32 bits. it's not an 'extension'. >>Because 'extensions' are hell slower. > >x86-64 is pretty much an 'extension' of x86-32. No it's completely different logics. it's not like rails of a train which you can simply widen a little (though that's not that easy either at crossings). You need to design completely new logics which is 64 bits. The additional problem you *directly* run into is that you can't clock it as high as you can clock a K7 cpu. Also a 64 bits cpu without plenty of registers is a major joke. If you can't get 128+ registers, instead of the 44 or so the K7 has, then such a 64 bits chip is not very serious for 64 bits applications! >>The compiler is not such a trivial thing. If you get 256 registers >>instead of EAX,EBX,EXC and another few others (with another 44 extra >>registers to use for register renaming etc) then the importance of the >>compiler is major. >> >>All the speedup has to come out of the compiler, *not* out of different >>programmed software of course. > >The compiler is important, but it's not going to be a huge thing to make a >compiler that emits decent x86-64 code, since it will be so close to existing >x86-32 code. It's not like it has 256 new registers to deal with - there are >only 8 more GP registers to deal with, and the fact that registers now hold 64 >bits. The compiler is the main problem for a new 64 bits chip. >>DIEP was very slow on the first alpha's, which is very irrelevant for >>the blazing fast plans that are on the board for Hammer and McKinley. >Have you even read the documentations for IA-64? You realize that the IA-64 is produced by intel and NOT by AMD? >>On paper diep should be very fast on McKinley and Hammer. In reality however >>both chips are not comparable. McKinley is 2 generations newer design >>than Hammer is. >And the compiler for McKinley will be about 6 generations behind. :) There are 2 compilers for mckinley AFAIK. One produced by intel, one produced by m$. So i'm not sure whether you find microsoft and intel compiler running behind, may i ask you which outdated language you write software in, microsoft basic date 1980? >>Suppose all AMD does is extend their FPU/MMX thing with >>some extra instructions. Then you have like 8 general MMX registers. >> >>That's not worth the effort of course. >> >>They need to make 128+ at least easily accessible 64 bits registers >>at least to make the chip interesting. Then they STILL are a generation >>behind on the McKinley. > >Do I need to keep asking if you've even read the documentation? x86-64 makes 16 >64-bit general-purpose registers available. It also adds some MMX/SSE/SSE2 >registers. Yeah the IA-64 documentation of microsoft for a hammer produced by AMD, you're funny! >>With so many registers the importance of the compiler gets overwhelming. >>It's more than a factor 2 a good compiler on such a chip. >> >>There are more issues. How big is the size of this chip going to get? > >Hammer is supposed to be some 103mm^2. McKinley is 464mm^2. >>Now the most important question: how high can they clock such a chip? >>The current plans on paper are simply not realistic. >Are you talking about Hammer here, or McKinley? Hammer, that the mckinley is fast and a real 64 bits cpu we already know! Hammer at most is a big PR offensive promoting a 32 bits chip being 64 bits, or a big failure as a native 64 bits chip. Best regards, Vincent
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