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Share correction history between threads
We did quite a few tests because this is a pretty involved change with unknown scaling behavior, but results are decent. [STC 10+0.1 1th, non-regression](https://tests.stockfishchess.org/tests/live_elo/6941ce3b46f342e1ec210180) ``` LLR: 2.93 (-2.94,2.94) <-1.75,0.25> Total: 83200 W: 21615 L: 21452 D: 40133 Ptnml(0-2): 247, 9064, 22844, 9169, 276 ``` [STC 5+0.05 8th](https://tests.stockfishchess.org/tests/live_elo/693dc38346f342e1ec20f555) ``` LLR: 3.48 (-2.94,2.94) <0.00,2.00> Total: 58536 W: 15067 L: 14688 D: 28781 Ptnml(0-2): 87, 6474, 15781, 6825, 101 ``` [LTC 20+0.2 8th](https://tests.stockfishchess.org/tests/live_elo/693f2afb46f342e1ec20f847) ``` LLR: 2.94 (-2.94,2.94) <0.50,2.50> Total: 27716 W: 7211 L: 6925 D: 13580 Ptnml(0-2): 8, 2674, 8207, 2962, 7 ``` [LTC 10+0.1 64th](https://tests.stockfishchess.org/tests/live_elo/694003aa46f342e1ec20fac4): ``` LLR: 2.94 (-2.94,2.94) <0.50,2.50> Total: 16918 W: 4439 L: 4182 D: 8297 Ptnml(0-2): 3, 1493, 5213, 1744, 6 ``` [NUMA test, 5+0.05 256th](https://tests.stockfishchess.org/tests/view/6941ee4e46f342e1ec210203) ``` LLR: 2.95 (-2.94,2.94) <0.00,2.00> Total: 7124 W: 1910 L: 1678 D: 3536 Ptnml(0-2): 0, 560, 2211, 790, 1 ``` [LTC 60+0.6 64th](https://tests.stockfishchess.org/tests/live_elo/6940a85346f342e1ec20fcde): ``` LLR: 2.94 (-2.94,2.94) <0.50,2.50> Total: 15504 W: 4045 L: 3826 D: 7633 Ptnml(0-2): 0, 1002, 5530, 1219, 1 ``` Bonus (courtesy of Viz): The 1 double kill in this last test was master blundering a cool mate in 3: https://lichess.org/jyNZuRl4 Basically the idea here is to share correction history between threads. That way, T1 can use the correction values produced by T2, which already searched positions with that pawn structure etc., so that T1 can search more efficiently. The table size per thread is about the same, so we shouldn't get a large increase in hash collisions; in fact, I'd expect a lower collision rate overall. Although I came up with and implemented the idea independently, [Caissa](https://github.com/Witek902/Caissa) was the first engine to implement corrhist sharing (and corrhist in the first place) – this idea is not completely novel. The table size is rounded to a power of two. In particular, it's `65536 * nextPowerOfTwo(threadCount)`. That way, the indexing operation becomes an AND of the key bits with a mask, rather than something more expensive (e.g., a `mul_hi64`-style approach or a modulo). The updates are racy, like the TT, but because `entry` is hoisted into a register, there's no risk of writing back a value that's out of the designated range `[-D, D]`. Various attempts at rewriting using atomics led to substantial slowdowns, so we begrudgingly ignored the functions in thread sanitizer, but at some point we'd like to make this better. We allocate one shared correction history per NUMA node, because the penalty associated with crossing nodes is substantial – I get a 40% hit with NPS=4 and 256 threads, which is intolerable. With separate tables per NUMA node I get a 6% penalty for nodes per second, which isn't ideal but apparently compensated for. closes https://github.com/official-stockfish/Stockfish/pull/6478 Bench: 2690604 Co-authored-by: Disservin <disservin.social@gmail.com>
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committed by
Disservin
co-authored by
Disservin
parent
fb41f2953f
commit
1a67ccc72e
+4
-3
@@ -33,6 +33,7 @@
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namespace Stockfish {
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class TranspositionTable;
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struct SharedHistories;
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// StateInfo struct stores information needed to restore a Position object to
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// its previous state when we retract a move. Whenever a move is made on the
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@@ -69,7 +70,6 @@ struct StateInfo {
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// elements are not invalidated upon list resizing.
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using StateListPtr = std::unique_ptr<std::deque<StateInfo>>;
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// Position class stores information regarding the board representation as
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// pieces, side to move, hash keys, castling info, etc. Important methods are
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// do_move() and undo_move(), used by the search to update node info when
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@@ -140,7 +140,8 @@ class Position {
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bool givesCheck,
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DirtyPiece& dp,
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DirtyThreats& dts,
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const TranspositionTable* tt);
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const TranspositionTable* tt,
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const SharedHistories* worker);
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void undo_move(Move m);
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void do_null_move(StateInfo& newSt, const TranspositionTable& tt);
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void undo_null_move();
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@@ -403,7 +404,7 @@ inline void Position::swap_piece(Square s, Piece pc, DirtyThreats* const dts) {
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inline void Position::do_move(Move m, StateInfo& newSt, const TranspositionTable* tt = nullptr) {
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new (&scratch_dts) DirtyThreats;
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do_move(m, newSt, gives_check(m), scratch_dp, scratch_dts, tt);
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do_move(m, newSt, gives_check(m), scratch_dp, scratch_dts, tt, nullptr);
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}
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inline StateInfo* Position::state() const { return st; }
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