runtime: convert schedt.npidle to atomic type

Note that this converts npidle from uint32 to int32 for consistency with
the other count fields in schedt and the type of p.id.

Note that this changes previously unsynchronized operations to
synchronized operations in:
  * handoffp
  * injectglist
  * schedtrace
  * schedEnableUser
  * sync_runtime_canSpin

For #53821.

Change-Id: I36d1b3b4a28131c9d47884fade6bc44439dd6937
Reviewed-on: https://go-review.googlesource.com/c/go/+/419445
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>

3 files changed, 16 insertions, 17 deletions

diff --git a/src/runtime/mgcpacer.go b/src/runtime/mgcpacer.go
index 24f856740e..9e12e4c8db 100644
--- a/src/runtime/mgcpacer.go
+++ b/src/runtime/mgcpacer.go
@@ -750,7 +750,7 @@ func (c *gcControllerState) enlistWorker() {
 	// If there are idle Ps, wake one so it will run an idle worker.
 	// NOTE: This is suspected of causing deadlocks. See golang.org/issue/19112.
 	//
-	//	if atomic.Load(&sched.npidle) != 0 && atomic.Load(&sched.nmspinning) == 0 {
+	//	if sched.npidle.Load() != 0 && atomic.Load(&sched.nmspinning) == 0 {
 	//		wakep()
 	//		return
 	//	}
diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index 55c82ffa3e..9cad2161b5 100644
--- a/src/runtime/proc.go
+++ b/src/runtime/proc.go
@@ -2362,7 +2362,7 @@ func handoffp(pp *p) {
 	}
 	// no local work, check that there are no spinning/idle M's,
 	// otherwise our help is not required
-	if atomic.Load(&sched.nmspinning)+atomic.Load(&sched.npidle) == 0 && atomic.Cas(&sched.nmspinning, 0, 1) { // TODO: fast atomic
+	if int32(atomic.Load(&sched.nmspinning))+sched.npidle.Load() == 0 && atomic.Cas(&sched.nmspinning, 0, 1) { // TODO: fast atomic
 		startm(pp, true)
 		return
 	}
@@ -2390,7 +2390,7 @@ func handoffp(pp *p) {
 	}
 	// If this is the last running P and nobody is polling network,
 	// need to wakeup another M to poll network.
-	if sched.npidle == uint32(gomaxprocs-1) && sched.lastpoll.Load() != 0 {
+	if sched.npidle.Load() == gomaxprocs-1 && sched.lastpoll.Load() != 0 {
 		unlock(&sched.lock)
 		startm(pp, false)
 		return
@@ -2410,7 +2410,7 @@ func handoffp(pp *p) {
 // Tries to add one more P to execute G's.
 // Called when a G is made runnable (newproc, ready).
 func wakep() {
-	if atomic.Load(&sched.npidle) == 0 {
+	if sched.npidle.Load() == 0 {
 		return
 	}
 	// be conservative about spinning threads
@@ -2649,8 +2649,7 @@ top:
 	// Limit the number of spinning Ms to half the number of busy Ps.
 	// This is necessary to prevent excessive CPU consumption when
 	// GOMAXPROCS>>1 but the program parallelism is low.
-	procs := uint32(gomaxprocs)
-	if mp.spinning || 2*atomic.Load(&sched.nmspinning) < procs-atomic.Load(&sched.npidle) {
+	if mp.spinning || int32(2*atomic.Load(&sched.nmspinning)) < gomaxprocs-sched.npidle.Load() {
 		if !mp.spinning {
 			mp.spinning = true
 			atomic.Xadd(&sched.nmspinning, 1)
@@ -3136,7 +3135,7 @@ func injectglist(glist *gList) {
 	*glist = gList{}
 
 	startIdle := func(n int) {
-		for ; n != 0 && sched.npidle != 0; n-- {
+		for ; n != 0 && sched.npidle.Load() != 0; n-- {
 			startm(nil, false)
 		}
 	}
@@ -3150,7 +3149,7 @@ func injectglist(glist *gList) {
 		return
 	}
 
-	npidle := int(atomic.Load(&sched.npidle))
+	npidle := int(sched.npidle.Load())
 	var globq gQueue
 	var n int
 	for n = 0; n < npidle && !q.empty(); n++ {
@@ -5156,9 +5155,9 @@ func sysmon() {
 		// from a timer to avoid adding system load to applications that spend
 		// most of their time sleeping.
 		now := nanotime()
-		if debug.schedtrace <= 0 && (sched.gcwaiting != 0 || atomic.Load(&sched.npidle) == uint32(gomaxprocs)) {
+		if debug.schedtrace <= 0 && (sched.gcwaiting != 0 || sched.npidle.Load() == gomaxprocs) {
 			lock(&sched.lock)
-			if atomic.Load(&sched.gcwaiting) != 0 || atomic.Load(&sched.npidle) == uint32(gomaxprocs) {
+			if atomic.Load(&sched.gcwaiting) != 0 || sched.npidle.Load() == gomaxprocs {
 				syscallWake := false
 				next := timeSleepUntil()
 				if next > now {
@@ -5318,7 +5317,7 @@ func retake(now int64) uint32 {
 			// On the one hand we don't want to retake Ps if there is no other work to do,
 			// but on the other hand we want to retake them eventually
 			// because they can prevent the sysmon thread from deep sleep.
-			if runqempty(pp) && atomic.Load(&sched.nmspinning)+atomic.Load(&sched.npidle) > 0 && pd.syscallwhen+10*1000*1000 > now {
+			if runqempty(pp) && atomic.Load(&sched.nmspinning)+uint32(sched.npidle.Load()) > 0 && pd.syscallwhen+10*1000*1000 > now {
 				continue
 			}
 			// Drop allpLock so we can take sched.lock.
@@ -5409,7 +5408,7 @@ func schedtrace(detailed bool) {
 	}
 
 	lock(&sched.lock)
-	print("SCHED ", (now-starttime)/1e6, "ms: gomaxprocs=", gomaxprocs, " idleprocs=", sched.npidle, " threads=", mcount(), " spinningthreads=", sched.nmspinning, " idlethreads=", sched.nmidle, " runqueue=", sched.runqsize)
+	print("SCHED ", (now-starttime)/1e6, "ms: gomaxprocs=", gomaxprocs, " idleprocs=", sched.npidle.Load(), " threads=", mcount(), " spinningthreads=", sched.nmspinning, " idlethreads=", sched.nmidle, " runqueue=", sched.runqsize)
 	if detailed {
 		print(" gcwaiting=", sched.gcwaiting, " nmidlelocked=", sched.nmidlelocked, " stopwait=", sched.stopwait, " sysmonwait=", sched.sysmonwait, "\n")
 	}
@@ -5505,7 +5504,7 @@ func schedEnableUser(enable bool) {
 		sched.disable.n = 0
 		globrunqputbatch(&sched.disable.runnable, n)
 		unlock(&sched.lock)
-		for ; n != 0 && sched.npidle != 0; n-- {
+		for ; n != 0 && sched.npidle.Load() != 0; n-- {
 			startm(nil, false)
 		}
 	} else {
@@ -5713,7 +5712,7 @@ func pidleput(pp *p, now int64) int64 {
 	idlepMask.set(pp.id)
 	pp.link = sched.pidle
 	sched.pidle.set(pp)
-	atomic.Xadd(&sched.npidle, 1)
+	sched.npidle.Add(1)
 	if !pp.limiterEvent.start(limiterEventIdle, now) {
 		throw("must be able to track idle limiter event")
 	}
@@ -5739,7 +5738,7 @@ func pidleget(now int64) (*p, int64) {
 		timerpMask.set(pp.id)
 		idlepMask.clear(pp.id)
 		sched.pidle = pp.link
-		atomic.Xadd(&sched.npidle, -1)
+		sched.npidle.Add(-1)
 		pp.limiterEvent.stop(limiterEventIdle, now)
 	}
 	return pp, now
@@ -6194,7 +6193,7 @@ func sync_runtime_canSpin(i int) bool {
 	// GOMAXPROCS>1 and there is at least one other running P and local runq is empty.
 	// As opposed to runtime mutex we don't do passive spinning here,
 	// because there can be work on global runq or on other Ps.
-	if i >= active_spin || ncpu <= 1 || gomaxprocs <= int32(sched.npidle+sched.nmspinning)+1 {
+	if i >= active_spin || ncpu <= 1 || gomaxprocs <= sched.npidle.Load()+int32(sched.nmspinning)+1 {
 		return false
 	}
 	if p := getg().m.p.ptr(); !runqempty(p) {
diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go
index bc482b00a2..7b43358ba1 100644
--- a/src/runtime/runtime2.go
+++ b/src/runtime/runtime2.go
@@ -778,7 +778,7 @@ type schedt struct {
 	ngsys atomic.Int32 // number of system goroutines
 
 	pidle      puintptr // idle p's
-	npidle     uint32
+	npidle     atomic.Int32
 	nmspinning uint32 // See "Worker thread parking/unparking" comment in proc.go.
 
 	// Global runnable queue.