This patch measures how frequently search is exploring new configurations.
This is done be computing a running average of ttHit. The ttHitAverage rate
is somewhat low (e.g. 30% for startpos) in the normal case, while it can be
very high if no progress is made (e.g. 90% for the fortress I used for testing).
This information can be used to influence search. In this patch, by adjusting
reductions if the rate > 50%. A first version (using a low ttHitAverageResolution
and this 50% threshold) passed testing:
STC
LLR: 2.96 (-2.94,2.94) [-1.50,4.50]
Total: 26425 W: 5837 L: 5650 D: 14938
http://tests.stockfishchess.org/tests/view/
5dcede8b0ebc5902563258fa
LTC
LLR: 2.96 (-2.94,2.94) [0.00,3.50]
Total: 32313 W: 5392 L: 5128 D: 21793
http://tests.stockfishchess.org/tests/view/
5dcefb1f0ebc590256325c0e
However, as discussed in pull request 2414, using a larger ttHitAverageResolution
gives a better approximation of the underlying distributions. This needs a slight
adjustment for the threshold as the new distributions are shifted a bit compared
to the older ones, and this threshold seemingly is sensitive (we used 0.53125 here).
https://github.com/official-stockfish/Stockfish/pull/2414
This final version also passed testing, and is used for the patch:
STC
LLR: 2.95 (-2.94,2.94) [-1.50,4.50]
Total: 16025 W: 3555 L: 3399 D: 9071
http://tests.stockfishchess.org/tests/view/
5dd070b90ebc5902579e20c2
LTC
LLR: 2.96 (-2.94,2.94) [0.00,3.50]
Total: 37576 W: 6277 L: 5998 D: 25301
http://tests.stockfishchess.org/tests/view/
5dd0f58e6f544e798086f224
Closes https://github.com/official-stockfish/Stockfish/pull/2414
Bench:
4989584
// Different node types, used as a template parameter
enum NodeType { NonPV, PV };
+ constexpr uint64_t ttHitAverageWindow = 4096;
+ constexpr uint64_t ttHitAverageResolution = 1024;
+
// Razor and futility margins
constexpr int RazorMargin = 661;
Value futility_margin(Depth d, bool improving) {
multiPV = std::max(multiPV, (size_t)4);
multiPV = std::min(multiPV, rootMoves.size());
+ ttHitAverage = ttHitAverageWindow * ttHitAverageResolution / 2;
int ct = int(Options["Contempt"]) * PawnValueEg / 100; // From centipawns
ttMove = rootNode ? thisThread->rootMoves[thisThread->pvIdx].pv[0]
: ttHit ? tte->move() : MOVE_NONE;
ttPv = PvNode || (ttHit && tte->is_pv());
+ // thisThread->ttHitAverage can be used to approximate the running average of ttHit
+ thisThread->ttHitAverage = (ttHitAverageWindow - 1) * thisThread->ttHitAverage / ttHitAverageWindow
+ + ttHitAverageResolution * ttHit;
// At non-PV nodes we check for an early TT cutoff
if ( !PvNode
{
Depth r = reduction(improving, depth, moveCount);
+ // Decrease reduction if the ttHit running average is large
+ if (thisThread->ttHitAverage > 544 * ttHitAverageResolution * ttHitAverageWindow / 1024)
+ r--;
+
// Reduction if other threads are searching this position.
if (th.marked())
r++;
Pawns::Table pawnsTable;
Material::Table materialTable;
size_t pvIdx, pvLast;
+ uint64_t ttHitAverage;
int selDepth, nmpMinPly;
Color nmpColor;
std::atomic<uint64_t> nodes, tbHits, bestMoveChanges;