Merge pull request #3953 from martin-frbg/issue3801

Do not use multithreading for small SYMV/SYR2K workloads

Author: martin-frbg

interface/symv.c

@@ -180,6 +180,9 @@ void CNAME(enum CBLAS_ORDER order, enum CBLAS_UPLO Uplo, blasint n, FLOAT alpha,
   buffer = (FLOAT *)blas_memory_alloc(1);
 
 #ifdef SMP
+  if (n <200)
+	  nthreads=1;
+  else
   nthreads = num_cpu_avail(2);
 
   if (nthreads == 1) {

interface/syr2k.c

@@ -368,6 +368,9 @@ void CNAME(enum CBLAS_ORDER order, enum CBLAS_UPLO Uplo, enum CBLAS_TRANSPOSE Tr
   mode |= (uplo  << BLAS_UPLO_SHIFT);
 
   args.common = NULL;
+  if (args.n*args.k <1000)
+	  args.nthreads =1 ;
+  else
   args.nthreads = num_cpu_avail(3);
 
   if (args.nthreads == 1) {