From 7955490de29ad5087904ce3a686243fe0230ac32 Mon Sep 17 00:00:00 2001
From: Rob Pike <r@golang.org>
Date: Thu, 6 Aug 2009 13:07:05 -0700
Subject: [PATCH] add runtime.GOMAXPROCS, allowing a program to, in effect, set
 $GOMAXPROCS

R=rsc
DELTA=29  (28 added, 1 deleted, 0 changed)
OCL=32829
CL=32837
---
 src/pkg/runtime/extern.go            |  3 +++
 src/pkg/runtime/proc.c               | 24 +++++++++++++++++++++++-
 test/bench/spectral-norm-parallel.go |  2 ++
 3 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/src/pkg/runtime/extern.go b/src/pkg/runtime/extern.go
index 1f6561394c..d002e48136 100644
--- a/src/pkg/runtime/extern.go
+++ b/src/pkg/runtime/extern.go
@@ -40,3 +40,6 @@ func LockOSThread()
 // If the calling goroutine has not called LockOSThread, UnlockOSThread is a no-op.
 func UnlockOSThread()
 
+// GOMAXPROCS sets the maximum number of CPUs that can be executing
+// simultaneously.   This call will go away when the scheduler improves.
+func GOMAXPROCS(n int)
diff --git a/src/pkg/runtime/proc.c b/src/pkg/runtime/proc.c
index 3c8ef54fe7..47356851b9 100644
--- a/src/pkg/runtime/proc.c
+++ b/src/pkg/runtime/proc.c
@@ -807,6 +807,29 @@ runtime·LockOSThread(void)
 	g->lockedm = m;
 }
 
+// delete when scheduler is stronger
+void
+runtime·GOMAXPROCS(int32 n)
+{
+	if(n < 1)
+		n = 1;
+
+	lock(&sched);
+	sched.gomaxprocs = n;
+	sched.mcpumax = n;
+	// handle fewer procs
+	while(sched.mcpu > sched.mcpumax) {
+		noteclear(&sched.stopped);
+		sched.waitstop = 1;
+		unlock(&sched);
+		notesleep(&sched.stopped);
+		lock(&sched);
+	}
+	// handle more procs
+	matchmg();
+	unlock(&sched);
+}
+
 void
 runtime·UnlockOSThread(void)
 {
@@ -821,4 +844,3 @@ runtime·mid(uint32 ret)
 	ret = m->id;
 	FLUSH(&ret);
 }
-
diff --git a/test/bench/spectral-norm-parallel.go b/test/bench/spectral-norm-parallel.go
index 0de2273ee7..9e7f33885f 100644
--- a/test/bench/spectral-norm-parallel.go
+++ b/test/bench/spectral-norm-parallel.go
@@ -40,6 +40,7 @@ import (
 	"flag";
 	"fmt";
 	"math";
+	"runtime";
 )
 
 var n = flag.Int("n", 2000, "count")
@@ -92,6 +93,7 @@ func (v Vec) ATimesTransp(u Vec) {
 
 func main() {
 	flag.Parse();
+	runtime.GOMAXPROCS(*nCPU);
 	N := *n;
 	u := make(Vec, N);
 	for i := 0; i < N; i++ {
-- 
2.48.1