Stockfish currently takes a while to clear the TT when using larger hash sizes.
On one machine with 128 GB hash it takes about 50 seconds with a single thread,
allowing it to use all allocated cores brought that time down to 4 seconds on
some Linux systems. The patch was further tested on Windows and refined with
NUMA binding of the hash initializing threads (we refer to pull request #1601
for the complete discussion and the speed measurements).
Closes https://github.com/official-stockfish/Stockfish/pull/1601
No functional change
#include <cstring> // For std::memset
#include <iostream>
#include <cstring> // For std::memset
#include <iostream>
TranspositionTable TT; // Our global transposition table
TranspositionTable TT; // Our global transposition table
/// TranspositionTable::clear() overwrites the entire transposition table
/// with zeros. It is called whenever the table is resized, or when the
/// user asks the program to clear the table (from the UCI interface).
/// TranspositionTable::clear() overwrites the entire transposition table
/// with zeros. It is called whenever the table is resized, or when the
/// user asks the program to clear the table (from the UCI interface).
+/// It starts as many threads as allowed by the Threads option.
void TranspositionTable::clear() {
void TranspositionTable::clear() {
- std::memset(table, 0, clusterCount * sizeof(Cluster));
-}
+ const size_t stride = clusterCount / Options["Threads"];
+ std::vector<std::thread> threads;
+ for (size_t idx = 0; idx < Options["Threads"]; idx++)
+ {
+ const size_t start = stride * idx,
+ len = idx != Options["Threads"] - 1 ?
+ stride :
+ clusterCount - start;
+ threads.push_back(std::thread([this, idx, start, len]() {
+ if (Options["Threads"] >= 8)
+ WinProcGroup::bindThisThread(idx);
+ std::memset(&table[start], 0, len * sizeof(Cluster));
+ }));
+ }
+ for (std::thread& th: threads)
+ th.join();
+}
/// TranspositionTable::probe() looks up the current position in the transposition
/// table. It returns true and a pointer to the TTEntry if the position is found.
/// TranspositionTable::probe() looks up the current position in the transposition
/// table. It returns true and a pointer to the TTEntry if the position is found.