# HG changeset patch
# User Merten Sach <msach@mailbox.tu-berlin.de>
# Date 1326451745 -3600
# Node ID c66137e4dc2f65ebdfbee157987e95cf86544511
# Parent  cf5faa15cb4d32633c81addff92664a5a08e6843
random wait time between tries to aquire master lock, because of performance penalties due to lock contention

diff -r cf5faa15cb4d -r c66137e4dc2f CoreLoop.c
--- a/CoreLoop.c	Tue Dec 20 19:42:42 2011 +0100
+++ b/CoreLoop.c	Fri Jan 13 11:49:05 2012 +0100
@@ -18,6 +18,9 @@
 
 void *terminateCoreLoop(VirtProcr *currVP);
 
+inline uint32_t
+randomNumber(uint32_t* seed1, uint32_t* seed2);
+
 /*This is the loop that runs in the OS Thread pinned to each core
  *Get virt procr from queue,
  * save state of current animator, then load in state of virt procr, using
@@ -45,6 +48,10 @@
    volatile int32 *masterLock;
    VirtProcr      *masterVP;
 
+   // init random number generator for retries
+   uint32_t seed1 = rand()%1000;
+   uint32_t seed2 = rand()%1000;
+
       //work-stealing struc on stack to prevent false-sharing in cache-line
    volatile GateStruc gate;
    //preGateProgress, waitProgress, exitProgress, gateClosed;
@@ -67,6 +74,8 @@
                          &suspendLock );
     }
    pthread_mutex_unlock( &suspendLock );
+   
+  //coreLoopThdParams->wait_iterations_hist = makeHistogram( 100, 0, 10000 );
 
       //printf( "\nCore unsuspended: %d\n", coreLoopThdParams->coreNum );
 
@@ -128,9 +137,15 @@
       #endif
       //=====================================================================
       int tries = 0; int gotLock = 0;
+      unsigned int wait_iterations=0;
       while( currVP == NULL ) //if queue was empty, enter get masterLock loop
        {    //queue was empty, so get master lock
 
+		 if(numMasterInARow > 2){
+		 	wait_iterations=(randomNumber(&seed1, &seed2) % (numMasterInARow*numMasterInARow))*100;
+	   		int i;
+	  	    for(i=0; i<wait_iterations; i++)/*busy wait*/;
+		 }
          gotLock = __sync_bool_compare_and_swap(masterLock,
                                                 UNLOCKED, LOCKED );
          if( gotLock )
@@ -142,11 +157,17 @@
              }
             numMasterInARow += 1;
             break;  //end while -- have a VP to animate now
-          }
+          }else{
+	   wait_iterations=(randomNumber(&seed1, &seed2) % (tries+1))*100;
+	   //addToHist( wait_iterations, coreLoopThdParams->wait_iterations_hist );
+	   int i;
+	   for(i=0; i<wait_iterations; i++)/*busy wait*/;
+	}
 
          tries++;      //if too many, means master on other core taking too long
          if( tries > MASTERLOCK_RETRIES ) { tries = 0; pthread_yield(); }
        }
+
       //============================= MEASUREMENT STUFF =====================
       #ifdef MEAS__TIME_MASTER_LOCK
       saveLowTimeStampCountInto( endStamp );
@@ -181,11 +202,19 @@
    }//CoreLoop      
  }
 
+inline uint32_t
+randomNumber(uint32_t* seed1, uint32_t* seed2){
+	*seed1 = 36969 * (*seed1 & 65535) + (*seed1 >> 16);
+	*seed2 = 18000 * (*seed2 & 65535) + (*seed2 >> 16);
+	return (*seed1 << 16) + *seed2;
+}
+
 
 void *
 terminateCoreLoop(VirtProcr *currVP){
    //first free shutdown VP that jumped here -- it first restores the
    // coreloop's stack, so addr of currVP in stack frame is still correct
+   //printHist(coreLoopThdParams[currVP->coreAnimatedBy]->wait_iterations_hist);
    VMS__dissipate_procr( currVP );
    pthread_exit( NULL );
 }