Author: Gerd Isenberg
Date: 07:38:42 12/04/03
Go up one level in this thread
On December 04, 2003 at 09:36:44, Robert Hyatt wrote:
>On December 04, 2003 at 00:36:17, Eugene Nalimov wrote:
>
>>On December 03, 2003 at 23:58:52, Robert Hyatt wrote:
>>
>>>On December 03, 2003 at 22:51:43, Sune Fischer wrote:
>>>
>>>>On December 03, 2003 at 16:58:17, Russell Reagan wrote:
>>>>
>>>>>On December 03, 2003 at 16:35:46, Slater Wold wrote:
>>>>>
>>>>>>What's the speedup between 1, 2, and 4 CPUs?
>>>>>
>>>>>After they (Bob and Eugene) did the NUMA stuff for Windows, 4 cpus was like a
>>>>>3.84x speedup.
>>>>>
>>>>>>Any idea on the speedup of going
>>>>>>to 64-bit?
>>>>>
>>>>>Clock for clock, Crafty is about 60% faster on 64-bit hardware. IE a 2GHz
>>>>>Opteron would run Crafty about 60% faster than a 2GHz 32-bit Athlon. Gian Carlo
>>>>>reported that Sjeng ran 70% faster, clock for clock.
>>>>
>>>>The Opteron has lots of improvements other than the 64 bit thing, so it is still
>>>>not exactly known what is contributing where for Crafty.
>>>>
>>>>I suspect Crafty would get a good speedup on a 32-bit Athlon too if it had 1 MB
>>>>cache and more registers, this should somehow be factored out.
>>>>
>>>>Granted that's not easy to do, but if/when we manage to take a handfull of
>>>>bitboard programs and compare their speedup to a handfull of non-bitboard
>>>>programs, then we might get a better impression of how much the 64-bit thing is
>>>>an issue on the overall.
>>>>
>>>>It is also possible that the first generation chess programs and compilers won't
>>>>be optimal. First tests are often 'worst case' senarios.
>>>>
>>>>-S.
>>>
>>>
>>>The thing that was most revealing was the 32 vs 64 bit stuff. Things like
>>>FirstOne() are a bit messy on 32 bit machines. On the Opteron it is dirt
>>>simple:
>>>
>>>int static __inline__ FirstOne(long word) {
>>> long dummy, dummy2;
>>> asm (
>>> " bsrq %0, %1" "\n\t"
>>> " jnz 1f" "\n\t"
>>> " movq $-1, %1" "\n\t"
>>> "1: movq $63, %0" "\n\t"
>>> " subq %1, %0" "\n\t"
>>> : "=r&" (dummy), "=r&" (dummy2)
>>> : "0" ((long) (word))
>>> : "cc");
>>> return (dummy);
>>>}
>>>
>>>bsrq is bsr for 64 bits. I use the "safe" version that does a test to see
>>>if no bits were set. If so, I skip the move -1 to a register and leave that
>>>register as set by bsfq. The 32 bit version is more than twice as long.
>>>I will get rid of the jump with a cmovq later, but I just didn't feel like
>>>fooling with it after I initially got it working.
>>
>>Here conditional move will be slower.
>>
>>Thanks,
>>Eugene
>
>
>OK, I'll bite. What's the explanation? :)
~100% correct branch prediction, because it's most often or always used with
none empty sets? I guess CMOV with todays branch prediction heuristics only pays
off if conditions are really random.
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