From 2f760cdf8dba05feb2c964b5f3b3339f0567a3c0 Mon Sep 17 00:00:00 2001
From: Marco Costalba <mcostalba@gmail.com>
Date: Wed, 3 Jun 2009 10:19:29 +0200
Subject: [PATCH] Document variables with heavy SMP read access

Also move NodesSincePoll away from the same cache line
of other heavy read accessed only variables.

Fortunatly we don't have anymore write access contention,
but still read access contention in some cases.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
---
 src/search.cpp | 29 +++++++++++++++--------------
 1 file changed, 15 insertions(+), 14 deletions(-)

diff --git a/src/search.cpp b/src/search.cpp
index 66bdb9b8..a6e2c341 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -130,8 +130,11 @@ namespace {
 
   /// Constants
 
+  // Search depth at iteration 1
+  const Depth InitialDepth = OnePly /*+ OnePly/2*/;
+
   // Depth limit for selective search
-  const Depth SelectiveDepth = 7*OnePly;
+  const Depth SelectiveDepth = 7 * OnePly;
 
   // Use internal iterative deepening?
   const bool UseIIDAtPVNodes = true;
@@ -187,12 +190,11 @@ namespace {
 
   /// Variables initialized from UCI options
 
-  // Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV
-  // nodes
-  int LMRPVMoves, LMRNonPVMoves;
+  // Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV nodes
+  int LMRPVMoves, LMRNonPVMoves; // heavy SMP read access for the latter
 
   // Depth limit for use of dynamic threat detection
-  Depth ThreatDepth;
+  Depth ThreatDepth; // heavy SMP read access
 
   // Last seconds noise filtering (LSN)
   bool UseLSNFiltering;
@@ -201,19 +203,13 @@ namespace {
   Value LSNValue;
 
   // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
+  // There is heavy SMP read access on these arrays
   Depth CheckExtension[2], SingleReplyExtension[2], PawnPushTo7thExtension[2];
   Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
 
-  // Search depth at iteration 1
-  const Depth InitialDepth = OnePly /*+ OnePly/2*/;
-
-  // Node counters, used only by thread[0]
-  int NodesSincePoll;
-  int NodesBetweenPolls = 30000;
-
   // Iteration counters
   int Iteration;
-  BetaCounterType BetaCounter; // does not have internal data
+  BetaCounterType BetaCounter; // has per-thread internal data
 
   // Scores and number of times the best move changed for each iteration
   IterationInfoType IterationInfo[PLY_MAX_PLUS_2];
@@ -231,7 +227,7 @@ namespace {
   bool InfiniteSearch;
   bool PonderSearch;
   bool StopOnPonderhit;
-  bool AbortSearch;
+  bool AbortSearch; // heavy SMP read access
   bool Quit;
   bool FailHigh;
   bool FailLow;
@@ -263,6 +259,11 @@ namespace {
   HANDLE SitIdleEvent[THREAD_MAX];
 #endif
 
+  // Node counters, used only by thread[0] but try to keep in different
+  // cache lines (64 bytes each) from the heavy SMP read accessed variables.
+  int NodesSincePoll;
+  int NodesBetweenPolls = 30000;
+
 
   /// Functions
 
-- 
2.39.2