From 652a8874b523360a3b19c5003c8ba9894ac54d0f Mon Sep 17 00:00:00 2001
From: "Robert Nurnberg @ elitebook" <robert.nurnberg@gmx.de>
Date: Fri, 14 Mar 2025 20:32:38 +0100
Subject: [PATCH] Allow more than 1024 threads on high-end machines

closes https://github.com/official-stockfish/Stockfish/pull/5929

No functional change
---
 src/engine.cpp | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/src/engine.cpp b/src/engine.cpp
index 6c8799a1..a4c0bb1e 100644
--- a/src/engine.cpp
+++ b/src/engine.cpp
@@ -18,6 +18,7 @@
 
 #include "engine.h"
 
+#include <algorithm>
 #include <cassert>
 #include <deque>
 #include <iosfwd>
@@ -32,6 +33,7 @@
 #include "misc.h"
 #include "nnue/network.h"
 #include "nnue/nnue_common.h"
+#include "numa.h"
 #include "perft.h"
 #include "position.h"
 #include "search.h"
@@ -44,8 +46,9 @@ namespace Stockfish {
 
 namespace NN = Eval::NNUE;
 
-constexpr auto StartFEN  = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1";
-constexpr int  MaxHashMB = Is64Bit ? 33554432 : 2048;
+constexpr auto StartFEN   = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1";
+constexpr int  MaxHashMB  = Is64Bit ? 33554432 : 2048;
+int            MaxThreads = std::max(1024, 4 * int(get_hardware_concurrency()));
 
 Engine::Engine(std::optional<std::string> path) :
     binaryDirectory(path ? CommandLine::get_binary_directory(*path) : ""),
@@ -74,7 +77,7 @@ Engine::Engine(std::optional<std::string> path) :
       }));
 
     options.add(  //
-      "Threads", Option(1, 1, 1024, [this](const Option&) {
+      "Threads", Option(1, 1, MaxThreads, [this](const Option&) {
           resize_threads();
           return thread_allocation_information_as_string();
       }));