From: Marco Costalba <mcostalba@gmail.com>
Date: Tue, 26 Jan 2010 11:05:38 +0000 (+0100)
Subject: Reduce lock contention in sp_search_pv()
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=cf9bf4e58fba6f478f3263412d224a4499f3fad6

Reduce lock contention in sp_search_pv()

In less then 1% of cases value > sp->bestValue, so avoid
an useless lock in the common case. This is the same change
already applied to sp_search().

Also SplitPoint futilityValue is not volatile because
never changes after has been assigned in split()

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
---

diff --git a/src/search.cpp b/src/search.cpp
index 7c341f87..8c5319b2 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -2046,37 +2046,40 @@ namespace {
           break;
 
       // New best move?
-      lock_grab(&(sp->lock));
-      if (value > sp->bestValue && !thread_should_stop(threadID))
+      if (value > sp->bestValue) // Less then 2% of cases
       {
-          sp->bestValue = value;
-          if (value > sp->alpha)
+          lock_grab(&(sp->lock));
+          if (value > sp->bestValue && !thread_should_stop(threadID))
           {
-              // Ask threads to stop before to modify sp->alpha
-              if (value >= sp->beta)
+              sp->bestValue = value;
+              if (value > sp->alpha)
               {
-                  for (int i = 0; i < ActiveThreads; i++)
-                      if (i != threadID && (i == sp->master || sp->slaves[i]))
-                          Threads[i].stop = true;
+                  // Ask threads to stop before to modify sp->alpha
+                  if (value >= sp->beta)
+                  {
+                      for (int i = 0; i < ActiveThreads; i++)
+                          if (i != threadID && (i == sp->master || sp->slaves[i]))
+                              Threads[i].stop = true;
 
-                  sp->finished = true;
-              }
+                      sp->finished = true;
+                  }
 
-              sp->alpha = value;
+                  sp->alpha = value;
 
-              sp_update_pv(sp->parentSstack, ss, sp->ply);
-              if (value == value_mate_in(sp->ply + 1))
-                  ss[sp->ply].mateKiller = move;
-        }
-        // If we are at ply 1, and we are searching the first root move at
-        // ply 0, set the 'Problem' variable if the score has dropped a lot
-        // (from the computer's point of view) since the previous iteration.
-        if (   sp->ply == 1
-            && Iteration >= 2
-            && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
-            Problem = true;
+                  sp_update_pv(sp->parentSstack, ss, sp->ply);
+                  if (value == value_mate_in(sp->ply + 1))
+                      ss[sp->ply].mateKiller = move;
+              }
+              // If we are at ply 1, and we are searching the first root move at
+              // ply 0, set the 'Problem' variable if the score has dropped a lot
+              // (from the computer's point of view) since the previous iteration.
+              if (   sp->ply == 1
+                     && Iteration >= 2
+                     && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
+                  Problem = true;
+          }
+          lock_release(&(sp->lock));
       }
-      lock_release(&(sp->lock));
     }
 
     lock_grab(&(sp->lock));
diff --git a/src/thread.h b/src/thread.h
index d0c1d8e9..899ccfe9 100644
--- a/src/thread.h
+++ b/src/thread.h
@@ -51,7 +51,8 @@ struct SplitPoint {
   SearchStack *parentSstack;
   int ply;
   Depth depth;
-  volatile Value alpha, beta, bestValue, futilityValue;
+  volatile Value alpha, beta, bestValue;
+  Value futilityValue;
   bool pvNode;
   int master, slaves[THREAD_MAX];
   Lock lock;