From 156e8b306d009ef118a4138f34098c8c41976a08 Mon Sep 17 00:00:00 2001
From: Dmitriy Vyukov <dvyukov@google.com>
Date: Wed, 31 Jul 2013 19:59:27 +0400
Subject: [PATCH] runtime: do not park sysmon thread if any goroutines are
 running Sysmon thread parks if no goroutines are running
 (runtime.sched.npidle == runtime.gomaxprocs). Currently it's unparked when a
 goroutine enters syscall, it was enough to retake P's from blocking syscalls.
 But it's not enough for reliable goroutine preemption. We need to ensure that
 sysmon runs if any goroutines are running.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/12167043
---
 src/pkg/runtime/proc.c | 30 ++++++++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/src/pkg/runtime/proc.c b/src/pkg/runtime/proc.c
index c4b8c02517..f333fdd877 100644
--- a/src/pkg/runtime/proc.c
+++ b/src/pkg/runtime/proc.c
@@ -1536,6 +1536,10 @@ exitsyscallfast(void)
 	if(runtime·sched.pidle) {
 		runtime·lock(&runtime·sched);
 		p = pidleget();
+		if(p && runtime·atomicload(&runtime·sched.sysmonwait)) {
+			runtime·atomicstore(&runtime·sched.sysmonwait, 0);
+			runtime·notewakeup(&runtime·sched.sysmonnote);
+		}
 		runtime·unlock(&runtime·sched);
 		if(p) {
 			acquirep(p);
@@ -1559,6 +1563,10 @@ exitsyscall0(G *gp)
 	p = pidleget();
 	if(p == nil)
 		globrunqput(gp);
+	else if(runtime·atomicload(&runtime·sched.sysmonwait)) {
+		runtime·atomicstore(&runtime·sched.sysmonwait, 0);
+		runtime·notewakeup(&runtime·sched.sysmonnote);
+	}
 	runtime·unlock(&runtime·sched);
 	if(p) {
 		acquirep(p);
@@ -1924,24 +1932,38 @@ static struct {
 	uintptr pcbuf[100];
 } prof;
 
+static void
+System(void)
+{
+}
+
 // Called if we receive a SIGPROF signal.
 void
 runtime·sigprof(uint8 *pc, uint8 *sp, uint8 *lr, G *gp)
 {
 	int32 n;
+	bool traceback;
 
-	// Windows does profiling in a dedicated thread w/o m.
-	if(!Windows && (m == nil || m->mcache == nil))
-		return;
 	if(prof.fn == nil || prof.hz == 0)
 		return;
+	traceback = true;
+	// Windows does profiling in a dedicated thread w/o m.
+	if(!Windows && (m == nil || m->mcache == nil))
+		traceback = false;
+	if(gp == m->g0 || gp == m->gsignal)
+		traceback = false;
+	if(m != nil && m->racecall)
+		traceback = false;
 
 	runtime·lock(&prof);
 	if(prof.fn == nil) {
 		runtime·unlock(&prof);
 		return;
 	}
-	n = runtime·gentraceback((uintptr)pc, (uintptr)sp, (uintptr)lr, gp, 0, prof.pcbuf, nelem(prof.pcbuf), nil, nil, false);
+	n = 1;
+	prof.pcbuf[0] = (uintptr)pc;
+	if(traceback)
+		n = runtime·gentraceback((uintptr)pc, (uintptr)sp, (uintptr)lr, gp, 0, prof.pcbuf, nelem(prof.pcbuf), nil, nil, false);
 	if(n > 0)
 		prof.fn(prof.pcbuf, n);
 	runtime·unlock(&prof);
-- 
2.48.1