From: Dmitriy Vyukov <dvyukov@google.com>
Date: Wed, 31 Jul 2013 15:59:27 +0000 (+0400)
Subject: runtime: do not park sysmon thread if any goroutines are running
X-Git-Tag: go1.2rc2~869
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=156e8b306d009ef118a4138f34098c8c41976a08;p=gostls13.git

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
---

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);