This reverts my earlier change that only the root node gets to output best move after fixing problem with MPI_Allreduce by our custom operator(BestMoveOp). This function is not commutable and we must ensure that its output is consistent among all nodes.
Previous behavior was to wait on all nodes to finish their search on their own TM and aggregate to root node via a blocking MPI_Allreduce call. This seems to be problematic.
In this commit a proper non-blocking signalling barrier was implemented to use TM from root node to control the cluster search, and disable TM on all non-root nodes.
Also includes some cosmetic fix to the nodes/NPS display.
When iterating through 'SYSTEM_LOGICAL_PROCESSOR_INFORMATION_EX' structure, do not use structure member beyond known size.
API is guaranteed to provide us at lease one element upon successful, and no element in the structure can have a zero size.
No functional change.
This pull request fixes a rare crashing bug on Windows inside our NUMA code, first
reported by Dann Corbit in the following forum thread (thanks!):
https://groups.google.com/forum/?fromgroups=#!topic/fishcooking/gA6aoMEuOwg
The fix is to not use structure member beyond known size when iterating through
'SYSTEM_LOGICAL_PROCESSOR_INFORMATION_EX' structure. We note that the Microsoft
API is guaranteed to provide us at least one element upon successful, and no
element in the structure can have a zero size.
No functional change.
This is the first patch teaching Stockfish how to use the 7-pieces
Syzygy tablebase currently calculated by Bujun Guo (@noobpwnftw) and
Ronald de Man (@syzygy1). The 7-pieces database are so big that they
required a change in the internal format of the files (technically,
some DTZ values are 16 bits long, so this had to be stored as wide
integers in the Huffman tree).
Here are the estimated file size for the 7-pieces Syzygy files,
compared to the 151G of the 6-pieces Syzygy:
```
7.1T ./7men_testing/4v3_pawnful (ongoing, 120 of 325 sets remaining)
2.4T ./7men_testing/4v3_pawnless
2.3T ./7men_testing/5v2_pawnful
660G ./7men_testing/5v2_pawnless
117G ./7men_testing/6v1_pawnful
87G ./7men_testing/6v1_pawnless
```
Some pointers to download or recalculate the tables:
Location of original files, by Bujun Guo:
ftp://ftp.chessdb.cn/pub/syzygy/
Mirrors:
http://tablebase.sesse.net/ (partial)
http://tablebase.lichess.ovh/tables/standard/7/
Generator code:
https://github.com/syzygy1/tb/
Closes https://github.com/official-stockfish/Stockfish/pull/1707
Bench: 5591925 (No functional change if SyzygyTB is not used)
----------------------
Comment by Leonardo Ljubičić (@DragonMist)
This is an amazing achievement, generating and being able to use 7 men syzygy
on the fly. Thank you for your efforts @noobpwnftw !! Looking forward how this
will work in real life, and expecting some trade off between gaining perfect
play and slow disc Access, but once the disc speed and space is not a problem,
I expect 7 men to yield something like 30 elo at least.
-----------------------
Comment by Michael Byrne (@MichaelB7)
This definitely has a bright future. I turned off the 50 move rule (ala ICCF
new rules) for the following position: `[d]8/8/1b6/8/4N2r/1k6/7B/R1K5 w - - 0 1`
This position is a 451 ply win for white (sans the 50 move rule, this position
was identified by the generator as the longest cursed win for white in KRBN v KRB).
Now Stockfish finds it instantly (as it should), nice work 👊👍 .
```
dep score nodes time
7 +132.79 4339 0:00.00 Rb1+ Kc4 Nd6+ Kc5 Bg1+ Kxd6 Rxb6+ Kc7 Be3 Rh2 Bd4
6 +132.79 1652 0:00.00 Rb1+ Kc4 Nd2+ Kd5 Rxb6 Rxh2 Nf3 Rf2
5 +132.79 589 0:00.00 Rb1+ Kc4 Rxb6 Rxh2 Nf6 Rh1+ Kb2
4 +132.79 308 0:00.00 Rb1+ Kc4 Nd6+ Kc3 Rxb6 Rxh2
3 +132.79 88 0:00.00 Rb1+ Ka4 Nc3+ Ka5 Ra1+ Kb4 Ra4+ Kxc3 Rxh4
2 +132.79 54 0:00.00 Rb1+ Ka4 Nc3+ Ka5 Ra1+ Kb4
1 +132.7
```
