Author: Robert Hyatt
Date: 10:53:46 09/03/03
Go up one level in this thread
On September 03, 2003 at 13:38:30, Gian-Carlo Pascutto wrote:
>On September 03, 2003 at 13:11:40, Robert Hyatt wrote:
>
>>Why wouldn't they check it at the top of Search() each time they go
>>deeper? It is a local memory reference with no speed penalty whatsoever.
>
>Yes. But to set it, you need a remote one.
>
>--
>GCP
How often? Here are some stats from a long crafty game:
SMP-> split=6266 stop=875 data=19/64 cpu=10:00 elap=2:39
SMP-> split=3511 stop=440 data=16/64 cpu=5:20 elap=1:27
SMP-> split=3768 stop=524 data=17/64 cpu=5:45 elap=1:33
SMP-> split=1724 stop=275 data=13/64 cpu=3:59 elap=1:04
SMP-> split=4894 stop=671 data=15/64 cpu=3:55 elap=1:03
SMP-> split=2666 stop=420 data=15/64 cpu=3:51 elap=1:02
SMP-> split=3412 stop=683 data=17/64 cpu=3:46 elap=1:00
SMP-> split=3447 stop=476 data=15/64 cpu=3:55 elap=1:03
SMP-> split=2985 stop=345 data=19/64 cpu=1:13 elap=19.53
SMP-> split=11657 stop=1620 data=23/64 cpu=3:32 elap=58.12
SMP-> split=1928 stop=292 data=17/64 cpu=3:24 elap=57.08
SMP-> split=53912 stop=6999 data=30/64 cpu=32:06 elap=8:42
SMP-> split=9997 stop=1209 data=23/64 cpu=3:31 elap=56.69
SMP-> split=2966 stop=527 data=19/64 cpu=3:28 elap=55.49
"split" is the number of times a single processor noticed an idle processor
and forced it to "join in" and help. "stop" is the number of times one
processor told everybody else at a split point "stop, your results are not
needed."
These are for roughly 1 minute searches in a real game (level 0 30 15 I think).
The number of stops is _very_ low. How much overhead do you think you will
see in the worst case of 7000 stops? 7000 * 3 memory stores, which is maybe a
millisecond worst case? Best case is 275 * 3 stores, almost nothing.
As I said, the number of times one processor tells others to "stop" is _tiny_.
As it should be.
Anyone can run a 4-cpu test with crafty and just grab the above lines from a
log to see what their machine results look like.
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