From: Dmitriy Vyukov <dvyukov@google.com>
Date: Wed, 31 Jul 2013 16:09:03 +0000 (+0400)
Subject: runtime: do not park sysmon thread if any goroutines are running
X-Git-Tag: go1.2rc2~866
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=658d19a53f26865549653fb16f80a47ae552b4f0;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=rsc
CC=golang-dev
https://golang.org/cl/12176043
---

diff --git a/src/pkg/runtime/proc.c b/src/pkg/runtime/proc.c
index c4b8c02517..c3af1efaf3 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);