From da5894a2ed5ced13cbac1cf9209a9e3c5a9fc6e6 Mon Sep 17 00:00:00 2001
From: Andrew <16061801+brada4@users.noreply.github.com>
Date: Fri, 23 Nov 2018 16:08:15 +0100
Subject: [PATCH] Limit _AXPY threading due to observed regression with excess
 threads

---
 interface/axpy.c  | 8 ++++++++
 interface/zaxpy.c | 7 +++++++
 2 files changed, 15 insertions(+)

diff --git a/interface/axpy.c b/interface/axpy.c
index 39edea6af..ca3640fa6 100644
--- a/interface/axpy.c
+++ b/interface/axpy.c
@@ -46,6 +46,10 @@
 #else
 #define MULTI_THREAD_MINIMAL  10000
 #endif
+#if defined(ARCH_X86) || defined(ARCH_X86_64)
+#define MULTI_THREAD_MAX_NUM 2
+#endif
+
 #ifndef CBLAS
 
 void NAME(blasint *N, FLOAT *ALPHA, FLOAT *x, blasint *INCX, FLOAT *y, blasint *INCY){
@@ -91,7 +95,11 @@ void CNAME(blasint n, FLOAT alpha, FLOAT *x, blasint incx, FLOAT *y, blasint inc
   if (incx == 0 || incy == 0 || n <= MULTI_THREAD_MINIMAL)
 	  nthreads = 1;
   else
+#ifdef MULTI_THREAD_MAX_NUM
+	  nthreads = MIN(MULTI_THREAD_MAX_NUM,num_cpu_avail(1));
+#else
 	  nthreads = num_cpu_avail(1);
+#endif
 
   if (nthreads == 1) {
 #endif
diff --git a/interface/zaxpy.c b/interface/zaxpy.c
index 1a0259c96..9b5823aaf 100644
--- a/interface/zaxpy.c
+++ b/interface/zaxpy.c
@@ -46,6 +46,9 @@
 #else
 #define MULTI_THREAD_MINIMAL  10000
 #endif
+#if defined(ARCH_X86) || defined(ARCH_X86_64)
+#define MULTI_THREAD_MAX_NUM 2
+#endif
 #ifndef CBLAS
 
 void NAME(blasint *N, FLOAT *ALPHA, FLOAT *x, blasint *INCX, FLOAT *y, blasint *INCY){
@@ -98,7 +101,11 @@ void CNAME(blasint n, FLOAT *ALPHA, FLOAT *x, blasint incx, FLOAT *y, blasint in
   if (incx == 0 || incy == 0 || n <= MULTI_THREAD_MINIMAL)
 	  nthreads = 1;
   else
+#ifdef MULTI_THREAD_MAX_NUM
+          nthreads = MIN(MULTI_THREAD_MAX_NUM,num_cpu_avail(1));
+#else
 	  nthreads = num_cpu_avail(1);
+#endif
 
   if (nthreads == 1) {
 #endif