Reduce number of data partitions in n.

Author: Tim Moon

driver/level3/level3_thread.c

@@ -525,7 +525,7 @@ static int gemm_driver(blas_arg_t *args, BLASLONG *range_m, BLASLONG
   BLASLONG range_M_buffer[MAX_CPU_NUMBER + 2];
   BLASLONG range_N_buffer[MAX_CPU_NUMBER + 2];
   BLASLONG *range_M, *range_N;
-  BLASLONG num_cpu_m, num_cpu_n;
+  BLASLONG num_parts;
 
   BLASLONG nthreads = args -> nthreads;
 
@@ -596,16 +596,16 @@ static int gemm_driver(blas_arg_t *args, BLASLONG *range_m, BLASLONG
   }
 
   /* Partition m into nthreads_m regions */
-  num_cpu_m  = 0;
+  num_parts = 0;
   while (m > 0){
-    width = blas_quickdivide(m + nthreads_m - num_cpu_m - 1, nthreads_m - num_cpu_m);
+    width = blas_quickdivide(m + nthreads_m - num_parts - 1, nthreads_m - num_parts);
     m -= width;
     if (m < 0) width = width + m;
-    range_M[num_cpu_m + 1] = range_M[num_cpu_m] + width;
-    num_cpu_m ++;
+    range_M[num_parts + 1] = range_M[num_parts] + width;
+    num_parts ++;
   }
-  for (i = num_cpu_m; i < MAX_CPU_NUMBER; i++) {
-    range_M[i + 1] = range_M[num_cpu_m];
+  for (i = num_parts; i < MAX_CPU_NUMBER; i++) {
+    range_M[i + 1] = range_M[num_parts];
   }
 
   /* Initialize parameters for parallel execution */
@@ -637,16 +637,19 @@ static int gemm_driver(blas_arg_t *args, BLASLONG *range_m, BLASLONG
 
     /* Partition (a step of) n into nthreads regions */
     range_N[0] = js;
-    num_cpu_n  = 0;
+    num_parts  = 0;
     while (n > 0){
-      width = blas_quickdivide(n + nthreads - num_cpu_n - 1, nthreads - num_cpu_n);
+      width = blas_quickdivide(n + nthreads - num_parts - 1, nthreads - num_parts);
+      if (width < SWITCH_RATIO) {
+        width = SWITCH_RATIO;
+      }
       n -= width;
       if (n < 0) width = width + n;
-      range_N[num_cpu_n + 1] = range_N[num_cpu_n] + width;
-      num_cpu_n ++;
+      range_N[num_parts + 1] = range_N[num_parts] + width;
+      num_parts ++;
     }
-    for (j = num_cpu_n; j < MAX_CPU_NUMBER; j++) {
-      range_N[j + 1] = range_N[num_cpu_n];
+    for (j = num_parts; j < MAX_CPU_NUMBER; j++) {
+      range_N[j + 1] = range_N[num_parts];
     }
 
     /* Clear synchronization flags */
@@ -683,7 +686,7 @@ int CNAME(blas_arg_t *args, BLASLONG *range_m, BLASLONG *range_n, FLOAT *sa, FLO
     n = range_n[1] - range_n[0];
   }
 
-  /* CPU partitions in m should have at least SWITCH_RATIO rows */
+  /* Partitions in m should have at least SWITCH_RATIO rows */
   if (m < 2 * SWITCH_RATIO) {
     nthreads_m = 1;
   } else {
@@ -693,11 +696,11 @@ int CNAME(blas_arg_t *args, BLASLONG *range_m, BLASLONG *range_n, FLOAT *sa, FLO
     }
   }
 
-  /* At most one CPU partition in n should have less than nthreads_m columns */
-  if (n < nthreads_m) {
+  /* Partitions in n should have at most SWITCH_RATIO * nthreads_m columns */
+  if (n < SWITCH_RATIO * nthreads_m) {
     nthreads_n = 1;
   } else {
-    nthreads_n = blas_quickdivide(n + nthreads_m - 1, nthreads_m);
+    nthreads_n = (n + SWITCH_RATIO * nthreads_m - 1) / (SWITCH_RATIO * nthreads_m);
     if (nthreads_m * nthreads_n > args -> nthreads) {
       nthreads_n = blas_quickdivide(args -> nthreads, nthreads_m);
     }