Increase size of the pawns table by the factor 8. This decreases the number of recalculations of pawn structure information significantly (at least at LTC).
I have done measurements for different depths and pawn cache sizes.
First are given the number of pawn entry calculations are done (in parentheses is the frequency that a call to probe triggers a pawn entry calculation). The delta% are the percentage of less done pawn entry calculations in comparison to master
VSTC: bench 1 1 12
STC: bench 8 1 16
LTC: bench 64 1 20
VLTC: bench 512 1 24
VSTC STC LTC VLTC
master 82218(6%) 548935(6%) 2415422(7%) 9548071(7%)
pawncache*2 79859(6%) 492943(5%) 2084794(6%) 8275206(6%)
pawncache*4 78551(6%) 458758(5%) 1827770(5%) 7112531(5%)
pawncache*8 77963(6%) 439421(4%) 1649169(5%) 6128652(4%)
delta%(p2-m) -2.9% -10.2% -13.7% -13.3%
delta%(p4-m) -4.5% -16.4% -24.3% -25.5%
delta%(p8-m) -5.2% -20.0% -31.7% -35.8%
STC: (non-regression test because at STC the effect is smaller than at LTC)
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 22767 W: 5160 L: 5040 D: 12567
http://tests.stockfishchess.org/tests/view/5d00f6040ebc5925cf09c3e2
LTC:
LLR: 2.94 (-2.94,2.94) [0.00,4.00]
Total: 26340 W: 4524 L: 4286 D: 17530
http://tests.stockfishchess.org/tests/view/5d00a3810ebc5925cf09ba16
No functional change.
In pawn structures like white pawns f6,h6 against black pawns f7,g6,h7
the attack on the king is blocked by the own pawns. So decrease the
penalty for king safety.
See diagram and discussion in
https://github.com/official-stockfish/Stockfish/pull/1434
A sample position that this patch wants to avoid is the following
1rr2bk1/3q1p1p/2n1bPpP/pp1pP3/2pP4/P1P1B3/1PBQN1P1/1K3R1R w - - 0 1
White pawn storm on the king side was a disaster, it locked the king
side completely. Therefore, all the king tropism bonus that white have
on the king side are useless, and kingadjacent attacks too. Master
gives White a static +4.5 advantage, but White cannot win that game.
The patch is lowering this evaluation artefact.
STC:
LLR: 2.94 (-2.94,2.94) [0.00,5.00]
Total: 16467 W: 3750 L: 3537 D: 9180
http://tests.stockfishchess.org/tests/view/5a92102d0ebc590297cc87d0
LTC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 64242 W: 11130 L: 10745 D: 42367
http://tests.stockfishchess.org/tests/view/5a923dc80ebc590297cc8806
This version includes reformatting and speed optimization by Alain Savard.
Bench: 5643527
This is the sequel of the previous patch, we now let the parent node initialize
stat score to zero once for all grandchildren.
Initialize statScore to zero for the grandchildren of the current position.
So statScore is shared between all grandchildren and only the first grandchild
starts with statScore = 0. Later grandchildren start with the last calculated
statScore of the previous grandchild. This influences the reduction rules in
LMR which are based on the statScore of parent position.
Tests results against the previous patch:
STC:
LLR: 2.96 (-2.94,2.94) [0.00,4.00]
Total: 23676 W: 5417 L: 5157 D: 13102
http://tests.stockfishchess.org/tests/view/5a9423a90ebc590297cc8a46
LTC:
LLR: 2.96 (-2.94,2.94) [0.00,4.00]
Total: 35485 W: 6168 L: 5898 D: 23419
http://tests.stockfishchess.org/tests/view/5a9435550ebc590297cc8a54
Bench: 5643520
Let the parent node initialize stat score to zero once for all siblings.
Initialize statScore to zero for the children of the current position.
So statScore is shared between sibling positions and only the first sibling
starts with statScore = 0. Later siblings start with the last calculated
statScore of the previous sibling. This influences the reduction rules in
in LMR which are based on the statScore of parent position.
STC:
LLR: 2.96 (-2.94,2.94) [0.00,4.00]
Total: 22683 W: 5202 L: 4946 D: 12535
http://tests.stockfishchess.org/tests/view/5a93315f0ebc590297cc894f
LTC:
LLR: 2.95 (-2.94,2.94) [0.00,4.00]
Total: 48548 W: 8346 L: 8035 D: 32167
http://tests.stockfishchess.org/tests/view/5a933ba90ebc590297cc8962
Bench: 5833683
