runtime: simplify nobarrierWakeTime

Also use the simplified nobarrierWakeTime in findrunnable, as it no
longer needs the current time.

Change-Id: I77b125d6a184dde0aeb517fc068164c274f0a046
Reviewed-on: https://go-review.googlesource.com/c/go/+/266304
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>

2 files changed, 9 insertions, 19 deletions

diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index c97f4820da..939757f3a7 100644
--- a/src/runtime/proc.go
+++ b/src/runtime/proc.go
@@ -2659,18 +2659,9 @@ stop:
 	// checkTimers here because it calls adjusttimers which may need to allocate
 	// memory, and that isn't allowed when we don't have an active P.
 	for _, _p_ := range allpSnapshot {
-		// This is similar to nobarrierWakeTime, but minimizes calls to
-		// nanotime.
-		if atomic.Load(&_p_.adjustTimers) > 0 {
-			if now == 0 {
-				now = nanotime()
-			}
-			pollUntil = now
-		} else {
-			w := int64(atomic.Load64(&_p_.timer0When))
-			if w != 0 && (pollUntil == 0 || w < pollUntil) {
-				pollUntil = w
-			}
+		w := nobarrierWakeTime(_p_)
+		if w != 0 && (pollUntil == 0 || w < pollUntil) {
+			pollUntil = w
 		}
 	}
 	if pollUntil != 0 {
diff --git a/src/runtime/time.go b/src/runtime/time.go
index 99290f66d0..75b66f8492 100644
--- a/src/runtime/time.go
+++ b/src/runtime/time.go
@@ -742,16 +742,15 @@ func addAdjustedTimers(pp *p, moved []*timer) {
 // nobarrierWakeTime looks at P's timers and returns the time when we
 // should wake up the netpoller. It returns 0 if there are no timers.
 // This function is invoked when dropping a P, and must run without
-// any write barriers. Therefore, if there are any timers that needs
-// to be moved earlier, it conservatively returns the current time.
-// The netpoller M will wake up and adjust timers before sleeping again.
+// any write barriers.
 //go:nowritebarrierrec
 func nobarrierWakeTime(pp *p) int64 {
-	if atomic.Load(&pp.adjustTimers) > 0 {
-		return nanotime()
-	} else {
-		return int64(atomic.Load64(&pp.timer0When))
+	next := int64(atomic.Load64(&pp.timer0When))
+	nextAdj := int64(atomic.Load64(&pp.timerModifiedEarliest))
+	if next == 0 || (nextAdj != 0 && nextAdj < next) {
+		next = nextAdj
 	}
+	return next
 }
 
 // runtimer examines the first timer in timers. If it is ready based on now,