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Simplify thread selection

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The depth dependency in best thread selection no longer seems to gain sufficiently and so can be simplified away.

Passed non-reg STC SMP:
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 437904 W: 111841 L: 112051 D: 214012
Ptnml(0-2): 485, 49454, 119332, 49148, 533
https://tests.stockfishchess.org/tests/view/6a3158590d5d4b19d08055cd

Passed non-reg LTC SMP:
LLR: 3.11 (-2.94,2.94) <-1.75,0.25>
Total: 484778 W: 123864 L: 124093 D: 236821
Ptnml(0-2): 121, 49237, 143920, 48972, 139
https://tests.stockfishchess.org/tests/view/6a377f3ba4f63d3271af0920

closes https://github.com/official-stockfish/Stockfish/pull/6935

No functional change
This commit is contained in:
Robert Nurnberg @ elitebook
2026-07-03 20:24:56 +02:00
committed by Joost VandeVondele
parent 32619a0294
commit 9449162d58
1 changed files with 5 additions and 14 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/thread.cpp
+5 -14
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@@ -350,22 +350,17 @@ void ThreadPool::start_thinking(const OptionsMap& options,
Thread* ThreadPool::get_best_thread() const { Thread* ThreadPool::get_best_thread() const {
Thread* bestThread = threads.front().get(); Thread* bestThread = threads.front().get();
Value minScore = VALUE_NONE; Value minScore = VALUE_INFINITE;
std::unordered_map<Move, i64, Move::MoveHash> votes( std::unordered_map<Move, i64, Move::MoveHash> votes(
2 * std::min(size(), bestThread->worker->rootMoves.size())); 2 * std::min(size(), bestThread->worker->rootMoves.size()));
// Find the minimum score of all threads
for (auto&& th : threads) for (auto&& th : threads)
minScore = std::min(minScore, th->worker->rootMoves[0].score); minScore = std::min(minScore, th->worker->rootMoves[0].score);
// Vote according to score and depth, and select the best thread // Vote according to score, and select the best thread
auto thread_voting_value = [minScore](Thread* th) {
return (th->worker->rootMoves[0].score - minScore + 14) * int(th->worker->rootDepth);
};
for (auto&& th : threads) for (auto&& th : threads)
votes[th->worker->rootMoves[0].pv[0]] += thread_voting_value(th.get()); votes[th->worker->rootMoves[0].pv[0]] += th->worker->rootMoves[0].score - minScore + 14;
for (auto&& th : threads) for (auto&& th : threads)
{ {
@@ -383,11 +378,6 @@ Thread* ThreadPool::get_best_thread() const {
&& is_decisive(newThreadMove.score) && is_decisive(newThreadMove.score)
&& !newThreadMove.score_is_bound(); && !newThreadMove.score_is_bound();
// We make sure not to pick a thread with a truncated principal variation.
const bool betterVotingValue =
thread_voting_value(th.get()) * int(newThreadMove.pv.size() > 2)
> thread_voting_value(bestThread) * int(bestThreadMove.pv.size() > 2);
if (bestThreadDecisive) if (bestThreadDecisive)
{ {
// Make sure we pick the shortest mate / TB conversion. // Make sure we pick the shortest mate / TB conversion.
@@ -402,7 +392,8 @@ Thread* ThreadPool::get_best_thread() const {
else if (newThreadDecisive else if (newThreadDecisive
|| (!is_loss(newThreadMove.score) || (!is_loss(newThreadMove.score)
&& (newThreadMoveVote > bestThreadMoveVote && (newThreadMoveVote > bestThreadMoveVote
|| (newThreadMoveVote == bestThreadMoveVote && betterVotingValue)))) || (newThreadMoveVote == bestThreadMoveVote
&& newThreadMove.pv.size() > bestThreadMove.pv.size()))))
bestThread = th.get(); bestThread = th.get();
} }