runtime: convert gcController.idleMarkTime to atomic type

For #53821.

Change-Id: I2f2b462908096dacb97fba9973798036ea1d9b68
Reviewed-on: https://go-review.googlesource.com/c/go/+/417783
Run-TryBot: Michael Pratt <[email protected]>
Reviewed-by: Austin Clements <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: prattmic

src/runtime/align_runtime_test.go

@@ -22,7 +22,6 @@ var AtomicFields = []uintptr{
 	unsafe.Offsetof(schedt{}.pollUntil),
 	unsafe.Offsetof(schedt{}.timeToRun),
 	unsafe.Offsetof(gcControllerState{}.dedicatedMarkWorkersNeeded),
-	unsafe.Offsetof(gcControllerState{}.idleMarkTime),
 	unsafe.Offsetof(timeHistogram{}.underflow),
 	unsafe.Offsetof(profBuf{}.overflow),
 	unsafe.Offsetof(profBuf{}.overflowTime),

src/runtime/mgc.go

@@ -1106,7 +1106,7 @@ func gcMarkTermination() {
 			sweepTermCpu,
 			gcController.assistTime.Load(),
 			gcController.dedicatedMarkTime.Load() + gcController.fractionalMarkTime.Load(),
-			gcController.idleMarkTime,
+			gcController.idleMarkTime.Load(),
 			markTermCpu,
 		} {
 			if i == 2 || i == 3 {

src/runtime/mgcpacer.go

@@ -281,10 +281,9 @@ type gcControllerState struct {
 	// running.
 	fractionalMarkTime atomic.Int64
 
-	// idleMarkTime is the nanoseconds spent in idle marking
-	// during this cycle. This is updated atomically throughout
-	// the cycle.
-	idleMarkTime int64
+	// idleMarkTime is the nanoseconds spent in idle marking during this
+	// cycle. This is updated throughout the cycle.
+	idleMarkTime atomic.Int64
 
 	// markStartTime is the absolute start time in nanoseconds
 	// that assists and background mark workers started.
@@ -420,7 +419,7 @@ func (c *gcControllerState) startCycle(markStartTime int64, procs int, trigger g
 	c.assistTime.Store(0)
 	c.dedicatedMarkTime.Store(0)
 	c.fractionalMarkTime.Store(0)
-	c.idleMarkTime = 0
+	c.idleMarkTime.Store(0)
 	c.markStartTime = markStartTime
 
 	// TODO(mknyszek): This is supposed to be the actual trigger point for the heap, but
@@ -671,7 +670,7 @@ func (c *gcControllerState) endCycle(now int64, procs int, userForced bool) {
 	}
 	idleUtilization := 0.0
 	if assistDuration > 0 {
-		idleUtilization = float64(c.idleMarkTime) / float64(assistDuration*int64(procs))
+		idleUtilization = float64(c.idleMarkTime.Load()) / float64(assistDuration*int64(procs))
 	}
 	// Determine the cons/mark ratio.
 	//
@@ -910,7 +909,7 @@ func (c *gcControllerState) markWorkerStop(mode gcMarkWorkerMode, duration int64
 	case gcMarkWorkerFractionalMode:
 		c.fractionalMarkTime.Add(duration)
 	case gcMarkWorkerIdleMode:
-		atomic.Xaddint64(&c.idleMarkTime, duration)
+		c.idleMarkTime.Add(duration)
 		c.removeIdleMarkWorker()
 	default:
 		throw("markWorkerStop: unknown mark worker mode")