Author: Robert Hyatt
Date: 19:37:04 05/14/01
Go up one level in this thread
On May 14, 2001 at 20:14:46, Dann Corbit wrote:
>On May 14, 2001 at 19:50:25, Dieter Buerssner wrote:
>
>>On May 14, 2001 at 17:27:15, Dann Corbit wrote:
>>
>>>You should be aware that having an 8 CPU system will be incredibly expensive,
>>>and it won't blast everyone out of the water. Double CPU speed and you gain 50
>>>ELO. So if you can run 7 times faster, you have added 350 ELO, which is a lot
>>>but not insurmountable.
>>
>>I think, for your estimtion of added playing strength, you should do at least
>>log2(number_of_cpus)*50 instead of (number_of_cpus-1)*50 Elo ...
>
>I am wondering about this huge reduction. SMP loss is not nearly so great. I
>think also it makes possible a earlier (or conceivably later) discovery of a key
>position.
>
>I have not seen any indication that ELO gain drops off with exponential gain in
>speed. Perhaps there are studies of which I am not aware that indicate
>exponential increase in strength is sublinear in ELO improvement.
>
>Consider an 8 CPU system, with each CPU at 1GHz. We obviously won't get 8Ghz
>throughput, but we won't lose all that much either, because with interlocked
>exchange {which is all you really need for a chess game} contention will
>{should} be low.
>
>For this reason, I estimate the real loss will be only 1CPU out of 8 if
>programmed properly. By the logarithmic calculation, a 64 CPU system would
>provide only 6x performance, which means a 10% utilization. That seems absurdly
>low to me.
>
>>You are obviously aware, that other things will factor in, that may make this
>>estimation optimistic nevertheless. However, I agree, that for a SMP capable
>>program, 8 CPUs will add a lot of strenght.
>
>But only 3x faster than a single CPU system? You certainly must be assuming
>that there is a severe drop-off in ELO with added compute power.
>
>Generally quoted we see 40-80 ELO estimates for each doubling in CPU speed.
You are overlooking the exponential factor. 3x faster to get one ply deeper,
3x faster (9x total) to get 2 plies deeper...
ie if you say 2x faster = 50 Elo, then the 8 processor machine could be a
max of 8x faster, which is 3 doublings or 150 Elo total. In reality it will
be closer to 6 than to 8x.
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