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Subject: Re: Source code to measure it - there is something wrong

Author: Vincent Diepeveen

Date: 05:07:07 07/17/03

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On July 16, 2003 at 18:25:51, Robert Hyatt wrote:

>On July 16, 2003 at 16:12:45, Dieter Buerssner wrote:
>
>>On July 16, 2003 at 15:40:07, Gerd Isenberg wrote:
>>
>>>Yes i see, but to do exactly Vincent's sequence, calling RanrotA 100 million
>>>times in a loop, you need a rather huge list ;-)
>>
>>Hi Gerd, for 100 millions, I would need 400 Mb RAM (which I can). I need
>>100e6*sizeof(pointer). But thatis not really the point. My idea (one alternative
>>at least) is to start with a cyclic linked list, that just connects the elements
>>in order at first, and last entry goes back to start. Then use a typical card
>>shuffling routine, to randomize this list. If the mem is over 400 Mb, it would
>>mean, that we don't visit each cell. If it is lower, we will visit the cells
>>serveral timed. I would suspect, as long as memory is much bigger than cache
>>sizes, it makes little difference. But does it make a difference to lmbench type
>>sequential testing (with the same linked list method)?
>>
>>And, after all, we use virtual memory nowadays. Doesn't this include one more
>>indirection (done by hardware). Without knowing much about it, I wouldn't be
>>surprized, that hardware time for those indirections is needed more often with
>>the random access style pattern.
>
>You are talking about the TLB.
>
>The memory mapping hardware needs two memory references to compute a real
>address before it can be accessed.  The TLB keeps the most recent N of these
>things around.  If you go wild with random accessing, you will _certainly_
>make memory latency 3x what it should be, because the TLB entries are 100%
>useless.  Of course that is not sensible because 90+ percent of the memory
>references in a chess program are _not_ scattered all over memory.

I happen to have a special mode in diep to generate some statistics. This is the
difference between the stronger programs and the real amateurs.

As you can see from part of the data as quoted at a big depth around 6% of the
positions were in hashtable (that includes positions where you do not get a
cutoff but depth-i where i > 0 too). So 94% will have that 3x penalty of a slow
access to RAM.

Let's not forget a read to the evaluation table which stores evaluation (always
overwrite and 1 probe) and let's not forget also that pawnhashtable which you
put in crafty always to gigantic proportions.

Pawnhashtable in DIEP is very small. It doesn't store that much info in fact.
Only patterns that have to do with pawns and no other knowledge inside the
patterns. Here is a part of the statistics, note that the mainline is not when
the statistics get printed. Those are end of ply:

        05:03:59 175029 175k 0 0 3192432900 (2) 16 (2528,12926) 0.040 Nd4xc6 b7x
c6 b2-b3 e6-e5 f4xe5 d6xe5 Be2-c4 Bc8-g4 Qd1-c1 Qc7-a5 Qc1-e1 Be7-b4 Be3-d2 Qa5-
c7
depth=16 nps=175135 ttl=5088790298 aborted=930676670 (afh=2807,splits=15271) tim
e=29056.33s
Statistics ply=16 for Successful Hashing
  Eval:   perc= 14.03 hash=601232768 calls=4282359068 from which m-e=0
  Pawn:   perc= 91.40 hash=3364694961 calls=3681126300
Statistics Qsearch totally 4265810730 nodes (83.82) from which 2029063989 firstp
ly leafs
[snip]
[snip]
tot=0 remainsbest=0 cutsame=0 cutother=0
(0=9.07% 74696628) (1=64.21% 528475969) (2=16.13% 132814700) (3=7.65% 62972325)
(4=1.68% 13888078) (5=0.89% 7366238) (6=0.18% 1555420) (7=0.10% 897605)
(8=0.02% 173336) (9=0.01% 106509) (10=0.00% 17823) (11=0.00% 12133)
(12=0.00% 1602) (13=0.00% 1065) (14=0.00% 94) (15=0.00% 43)

total main search depth count = 822979568 (16.61)

>>
>>BTW. To shuffle a deck of N cards, one needs N calls to the PRNG. Often people,
>>who try this first, do it rather wrong. They randomly choose 2 indices, and swap
>>those cards. This is a very inefficient method, and even with many more than N
>>calls to the PRNG, the deck is not shuffled well.
>>
>>I did not start yet. When I have the results, I can think about possible
>>problems with mod, loop unrolling, etc. (I will use loop unrolling for the
>>random linked list test).
>>
>>Cheers,
>>Dieter



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