diff --git a/src/pkg/runtime/cpuprof.c b/src/pkg/runtime/cpuprof.c
index ef3077339a260..8117c9732af3b 100644
--- a/src/pkg/runtime/cpuprof.c
+++ b/src/pkg/runtime/cpuprof.c
@@ -331,7 +331,7 @@ getprofile(Profile *p)
 
 	if(p->wholding) {
 		// Release previous log to signal handling side.
-		// Loop because we are racing against setprofile(off).
+		// Loop because we are racing against SetCPUProfileRate(0).
 		for(;;) {
 			n = p->handoff;
 			if(n == 0) {
diff --git a/src/pkg/runtime/lock_futex.c b/src/pkg/runtime/lock_futex.c
index bb40b9255956c..42f37348a5251 100644
--- a/src/pkg/runtime/lock_futex.c
+++ b/src/pkg/runtime/lock_futex.c
@@ -83,11 +83,7 @@ runtime·lock(Lock *l)
 		if(v == MUTEX_UNLOCKED)
 			return;
 		wait = MUTEX_SLEEPING;
-		if(m->profilehz > 0)
-			runtime·setprof(false);
 		runtime·futexsleep((uint32*)&l->key, MUTEX_SLEEPING, -1);
-		if(m->profilehz > 0)
-			runtime·setprof(true);
 	}
 }
 
@@ -133,12 +129,8 @@ runtime·notesleep(Note *n)
 {
 	if(g != m->g0)
 		runtime·throw("notesleep not on g0");
-	if(m->profilehz > 0)
-		runtime·setprof(false);
 	while(runtime·atomicload((uint32*)&n->key) == 0)
 		runtime·futexsleep((uint32*)&n->key, 0, -1);
-	if(m->profilehz > 0)
-		runtime·setprof(true);
 }
 
 #pragma textflag 7
@@ -179,16 +171,11 @@ runtime·notetsleep(Note *n, int64 ns)
 	if(g != m->g0 && !m->gcing)
 		runtime·throw("notetsleep not on g0");
 
-	if(m->profilehz > 0)
-		runtime·setprof(false);
 	res = notetsleep(n, ns, 0, 0);
-	if(m->profilehz > 0)
-		runtime·setprof(true);
 	return res;
 }
 
 // same as runtime·notetsleep, but called on user g (not g0)
-// does not need to call runtime·setprof, because entersyscallblock does it
 // calls only nosplit functions between entersyscallblock/exitsyscall
 bool
 runtime·notetsleepg(Note *n, int64 ns)
diff --git a/src/pkg/runtime/lock_sema.c b/src/pkg/runtime/lock_sema.c
index ea7af1f91a527..e365db12bd6c0 100644
--- a/src/pkg/runtime/lock_sema.c
+++ b/src/pkg/runtime/lock_sema.c
@@ -81,11 +81,7 @@ runtime·lock(Lock *l)
 			}
 			if(v&LOCKED) {
 				// Queued.  Wait.
-				if(m->profilehz > 0)
-					runtime·setprof(false);
 				runtime·semasleep(-1);
-				if(m->profilehz > 0)
-					runtime·setprof(true);
 				i = 0;
 			}
 		}
@@ -164,11 +160,7 @@ runtime·notesleep(Note *n)
 		return;
 	}
 	// Queued.  Sleep.
-	if(m->profilehz > 0)
-		runtime·setprof(false);
 	runtime·semasleep(-1);
-	if(m->profilehz > 0)
-		runtime·setprof(true);
 }
 
 #pragma textflag 7
@@ -240,16 +232,11 @@ runtime·notetsleep(Note *n, int64 ns)
 	if(m->waitsema == 0)
 		m->waitsema = runtime·semacreate();
 
-	if(m->profilehz > 0)
-		runtime·setprof(false);
 	res = notetsleep(n, ns, 0, nil);
-	if(m->profilehz > 0)
-		runtime·setprof(true);
 	return res;
 }
 
 // same as runtime·notetsleep, but called on user g (not g0)
-// does not need to call runtime·setprof, because entersyscallblock does it
 // calls only nosplit functions between entersyscallblock/exitsyscall
 bool
 runtime·notetsleepg(Note *n, int64 ns)
diff --git a/src/pkg/runtime/os_darwin.c b/src/pkg/runtime/os_darwin.c
index db44e74cfb9c1..1a0b68dbf9eb3 100644
--- a/src/pkg/runtime/os_darwin.c
+++ b/src/pkg/runtime/os_darwin.c
@@ -12,7 +12,6 @@ extern SigTab runtime·sigtab[];
 
 static Sigset sigset_none;
 static Sigset sigset_all = ~(Sigset)0;
-static Sigset sigset_prof = 1<<(SIGPROF-1);
 
 static void
 unimplemented(int8 *name)
@@ -129,7 +128,6 @@ runtime·minit(void)
 	runtime·signalstack((byte*)m->gsignal->stackguard - StackGuard, 32*1024);
 
 	runtime·sigprocmask(SIG_SETMASK, &sigset_none, nil);
-	runtime·setprof(m->profilehz > 0);
 }
 
 // Called from dropm to undo the effect of an minit.
@@ -481,37 +479,6 @@ runtime·memlimit(void)
 	return 0;
 }
 
-// NOTE(rsc): On OS X, when the CPU profiling timer expires, the SIGPROF
-// signal is not guaranteed to be sent to the thread that was executing to
-// cause it to expire.  It can and often does go to a sleeping thread, which is
-// not interesting for our profile.  This is filed Apple Bug Report #9177434,
-// copied to http://code.google.com/p/go/source/detail?r=35b716c94225.
-// To work around this bug, we disable receipt of the profiling signal on
-// a thread while in blocking system calls.  This forces the kernel to deliver
-// the profiling signal to an executing thread.
-//
-// The workaround fails on OS X machines using a 64-bit Snow Leopard kernel.
-// In that configuration, the kernel appears to want to deliver SIGPROF to the
-// sleeping threads regardless of signal mask and, worse, does not deliver
-// the signal until the thread wakes up on its own.
-//
-// If necessary, we can switch to using ITIMER_REAL for OS X and handle
-// the kernel-generated SIGALRM by generating our own SIGALRMs to deliver
-// to all the running threads.  SIGALRM does not appear to be affected by
-// the 64-bit Snow Leopard bug.  However, as of this writing Mountain Lion
-// is in preview, making Snow Leopard two versions old, so it is unclear how
-// much effort we need to spend on one buggy kernel.
-
-// Control whether profiling signal can be delivered to this thread.
-void
-runtime·setprof(bool on)
-{
-	if(on)
-		runtime·sigprocmask(SIG_UNBLOCK, &sigset_prof, nil);
-	else
-		runtime·sigprocmask(SIG_BLOCK, &sigset_prof, nil);
-}
-
 void
 runtime·setsig(int32 i, GoSighandler *fn, bool restart)
 {
diff --git a/src/pkg/runtime/os_freebsd.c b/src/pkg/runtime/os_freebsd.c
index 386b4002c2a4c..a246c8794e248 100644
--- a/src/pkg/runtime/os_freebsd.c
+++ b/src/pkg/runtime/os_freebsd.c
@@ -233,12 +233,6 @@ runtime·memlimit(void)
 	return rl.rlim_cur - used;
 }
 
-void
-runtime·setprof(bool on)
-{
-	USED(on);
-}
-
 extern void runtime·sigtramp(void);
 
 typedef struct sigaction {
diff --git a/src/pkg/runtime/os_linux.c b/src/pkg/runtime/os_linux.c
index d940c9765bf8e..6b93b2f2df0c6 100644
--- a/src/pkg/runtime/os_linux.c
+++ b/src/pkg/runtime/os_linux.c
@@ -274,12 +274,6 @@ runtime·memlimit(void)
 	return rl.rlim_cur - used;
 }
 
-void
-runtime·setprof(bool on)
-{
-	USED(on);
-}
-
 #ifdef GOARCH_386
 #define sa_handler k_sa_handler
 #endif
diff --git a/src/pkg/runtime/os_netbsd.c b/src/pkg/runtime/os_netbsd.c
index 95c1070d1b236..684a94956b43c 100644
--- a/src/pkg/runtime/os_netbsd.c
+++ b/src/pkg/runtime/os_netbsd.c
@@ -271,12 +271,6 @@ runtime·memlimit(void)
 	return 0;
 }
 
-void
-runtime·setprof(bool on)
-{
-	USED(on);
-}
-
 extern void runtime·sigtramp(void);
 
 typedef struct sigaction {
diff --git a/src/pkg/runtime/os_openbsd.c b/src/pkg/runtime/os_openbsd.c
index bbb33a7f48754..eee8127dc6889 100644
--- a/src/pkg/runtime/os_openbsd.c
+++ b/src/pkg/runtime/os_openbsd.c
@@ -248,12 +248,6 @@ runtime·memlimit(void)
 	return 0;
 }
 
-void
-runtime·setprof(bool on)
-{
-	USED(on);
-}
-
 extern void runtime·sigtramp(void);
 
 typedef struct sigaction {
diff --git a/src/pkg/runtime/os_plan9.c b/src/pkg/runtime/os_plan9.c
index d97e5bc339766..e8e116f488265 100644
--- a/src/pkg/runtime/os_plan9.c
+++ b/src/pkg/runtime/os_plan9.c
@@ -322,12 +322,6 @@ runtime·memlimit(void)
 	return 0;
 }
 
-void
-runtime·setprof(bool on)
-{
-	USED(on);
-}
-
 #pragma dataflag 16 // no pointers
 static int8 badsignal[] = "runtime: signal received on thread not created by Go.\n";
 
diff --git a/src/pkg/runtime/os_windows.c b/src/pkg/runtime/os_windows.c
index ffd7e997e3091..0c3b4d961e456 100644
--- a/src/pkg/runtime/os_windows.c
+++ b/src/pkg/runtime/os_windows.c
@@ -474,12 +474,6 @@ runtime·memlimit(void)
 	return 0;
 }
 
-void
-runtime·setprof(bool on)
-{
-	USED(on);
-}
-
 #pragma dataflag 16 // no pointers
 int8 runtime·badsignalmsg[] = "runtime: signal received on thread not created by Go.\n";
 int32 runtime·badsignallen = sizeof runtime·badsignalmsg - 1;
diff --git a/src/pkg/runtime/pprof/pprof.go b/src/pkg/runtime/pprof/pprof.go
index 32c1098b9945b..5c1f3d460dbb8 100644
--- a/src/pkg/runtime/pprof/pprof.go
+++ b/src/pkg/runtime/pprof/pprof.go
@@ -20,8 +20,7 @@ import (
 	"text/tabwriter"
 )
 
-// BUG(rsc): A bug in the OS X Snow Leopard 64-bit kernel prevents
-// CPU profiling from giving accurate results on that system.
+// BUG(rsc): Profiles are incomplete and inaccuate on OS X. See http://golang.org/issue/6047 for details.
 
 // A Profile is a collection of stack traces showing the call sequences
 // that led to instances of a particular event, such as allocation.
diff --git a/src/pkg/runtime/pprof/pprof_test.go b/src/pkg/runtime/pprof/pprof_test.go
index 94d19f741c46d..995c2fe68d016 100644
--- a/src/pkg/runtime/pprof/pprof_test.go
+++ b/src/pkg/runtime/pprof/pprof_test.go
@@ -19,6 +19,38 @@ import (
 )
 
 func TestCPUProfile(t *testing.T) {
+	buf := make([]byte, 100000)
+	testCPUProfile(t, []string{"crc32.ChecksumIEEE"}, func() {
+		// This loop takes about a quarter second on a 2 GHz laptop.
+		// We only need to get one 100 Hz clock tick, so we've got
+		// a 25x safety buffer.
+		for i := 0; i < 1000; i++ {
+			crc32.ChecksumIEEE(buf)
+		}
+	})
+}
+
+func TestCPUProfileMultithreaded(t *testing.T) {
+	buf := make([]byte, 100000)
+	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(2))
+	testCPUProfile(t, []string{"crc32.ChecksumIEEE", "crc32.Update"}, func() {
+		c := make(chan int)
+		go func() {
+			for i := 0; i < 2000; i++ {
+				crc32.Update(0, crc32.IEEETable, buf)
+			}
+			c <- 1
+		}()
+		// This loop takes about a quarter second on a 2 GHz laptop.
+		// We only need to get one 100 Hz clock tick, so we've got
+		// a 25x safety buffer.
+		for i := 0; i < 2000; i++ {
+			crc32.ChecksumIEEE(buf)
+		}
+	})
+}
+
+func testCPUProfile(t *testing.T, need []string, f func()) {
 	switch runtime.GOOS {
 	case "darwin":
 		out, err := exec.Command("uname", "-a").CombinedOutput()
@@ -27,26 +59,16 @@ func TestCPUProfile(t *testing.T) {
 		}
 		vers := string(out)
 		t.Logf("uname -a: %v", vers)
-		// Lion uses "Darwin Kernel Version 11".
-		if strings.Contains(vers, "Darwin Kernel Version 10") && strings.Contains(vers, "RELEASE_X86_64") {
-			t.Skip("skipping test on known-broken kernel (64-bit Leopard / Snow Leopard)")
-		}
 	case "plan9":
 		// unimplemented
 		return
 	}
 
-	buf := make([]byte, 100000)
 	var prof bytes.Buffer
 	if err := StartCPUProfile(&prof); err != nil {
 		t.Fatal(err)
 	}
-	// This loop takes about a quarter second on a 2 GHz laptop.
-	// We only need to get one 100 Hz clock tick, so we've got
-	// a 25x safety buffer.
-	for i := 0; i < 1000; i++ {
-		crc32.ChecksumIEEE(buf)
-	}
+	f()
 	StopCPUProfile()
 
 	// Convert []byte to []uintptr.
@@ -56,6 +78,10 @@ func TestCPUProfile(t *testing.T) {
 	val = val[:l]
 
 	if l < 13 {
+		if runtime.GOOS == "darwin" {
+			t.Logf("ignoring failure on OS X; see golang.org/issue/6047")
+			return
+		}
 		t.Fatalf("profile too short: %#x", val)
 	}
 
@@ -69,7 +95,7 @@ func TestCPUProfile(t *testing.T) {
 	}
 
 	// Check that profile is well formed and contains ChecksumIEEE.
-	found := false
+	have := make([]uintptr, len(need))
 	for len(val) > 0 {
 		if len(val) < 2 || val[0] < 1 || val[1] < 1 || uintptr(len(val)) < 2+val[1] {
 			t.Fatalf("malformed profile.  leftover: %#x", val)
@@ -79,14 +105,38 @@ func TestCPUProfile(t *testing.T) {
 			if f == nil {
 				continue
 			}
-			if strings.Contains(f.Name(), "ChecksumIEEE") {
-				found = true
+			for i, name := range need {
+				if strings.Contains(f.Name(), name) {
+					have[i] += val[0]
+				}
 			}
 		}
 		val = val[2+val[1]:]
 	}
 
-	if !found {
-		t.Fatal("did not find ChecksumIEEE in the profile")
+	var total uintptr
+	for i, name := range need {
+		total += have[i]
+		t.Logf("%s: %d\n", name, have[i])
+	}
+	ok := true
+	if total == 0 {
+		t.Logf("no CPU profile samples collected")
+		ok = false
+	}
+	min := total / uintptr(len(have)) / 2
+	for i, name := range need {
+		if have[i] < min {
+			t.Logf("%s has %d samples out of %d, want at least %d, ideally %d", name, have[i], total, min, total/uintptr(len(have)))
+			ok = false
+		}
+	}
+
+	if !ok {
+		if runtime.GOOS == "darwin" {
+			t.Logf("ignoring failure on OS X; see golang.org/issue/6047")
+			return
+		}
+		t.FailNow()
 	}
 }
diff --git a/src/pkg/runtime/proc.c b/src/pkg/runtime/proc.c
index b0aa428e99b24..a8b98b73db97f 100644
--- a/src/pkg/runtime/proc.c
+++ b/src/pkg/runtime/proc.c
@@ -1384,9 +1384,6 @@ void
 	// but can have inconsistent g->sched, do not let GC observe it.
 	m->locks++;
 
-	if(m->profilehz > 0)
-		runtime·setprof(false);
-
 	// Leave SP around for gc and traceback.
 	save(runtime·getcallerpc(&dummy), runtime·getcallersp(&dummy));
 
@@ -1439,9 +1436,6 @@ void
 
 	m->locks++;  // see comment in entersyscall
 
-	if(m->profilehz > 0)
-		runtime·setprof(false);
-
 	// Leave SP around for gc and traceback.
 	save(runtime·getcallerpc(&dummy), runtime·getcallersp(&dummy));
 	g->gcsp = g->sched.sp;
@@ -1477,10 +1471,6 @@ runtime·exitsyscall(void)
 {
 	m->locks++;  // see comment in entersyscall
 
-	// Check whether the profiler needs to be turned on.
-	if(m->profilehz > 0)
-		runtime·setprof(true);
-
 	if(g->isbackground)  // do not consider blocked scavenger for deadlock detection
 		inclocked(-1);
 
diff --git a/src/pkg/runtime/runtime.h b/src/pkg/runtime/runtime.h
index cc389531354cc..c4beab1b5d88c 100644
--- a/src/pkg/runtime/runtime.h
+++ b/src/pkg/runtime/runtime.h
@@ -1043,16 +1043,6 @@ void	runtime·ifaceE2I(InterfaceType*, Eface, Iface*);
 
 uintptr	runtime·memlimit(void);
 
-// If appropriate, ask the operating system to control whether this
-// thread should receive profiling signals.  This is only necessary on OS X.
-// An operating system should not deliver a profiling signal to a
-// thread that is not actually executing (what good is that?), but that's
-// what OS X prefers to do.  When profiling is turned on, we mask
-// away the profiling signal when threads go to sleep, so that OS X
-// is forced to deliver the signal to a thread that's actually running.
-// This is a no-op on other systems.
-void	runtime·setprof(bool);
-
 // float.c
 extern float64 runtime·nan;
 extern float64 runtime·posinf;
diff --git a/src/pkg/runtime/signal_unix.c b/src/pkg/runtime/signal_unix.c
index 54e461f995f73..8bc7b8401b3f1 100644
--- a/src/pkg/runtime/signal_unix.c
+++ b/src/pkg/runtime/signal_unix.c
@@ -83,13 +83,11 @@ runtime·resetcpuprofiler(int32 hz)
 	runtime·memclr((byte*)&it, sizeof it);
 	if(hz == 0) {
 		runtime·setitimer(ITIMER_PROF, &it, nil);
-		runtime·setprof(false);
 	} else {
 		it.it_interval.tv_sec = 0;
 		it.it_interval.tv_usec = 1000000 / hz;
 		it.it_value = it.it_interval;
 		runtime·setitimer(ITIMER_PROF, &it, nil);
-		runtime·setprof(true);
 	}
 	m->profilehz = hz;
 }