runtime: avoid unnecessary netpoll wakeups during timer creation

goos: linux
goarch: amd64
pkg: time
cpu: AMD Ryzen 9 7950X 16-Core Processor
                                   │ s7base.txt  │               s7.txt               │
                                   │   sec/op    │   sec/op     vs base               │
AdjustTimers10000-32                 315.1µ ± 4%   291.4µ ± 5%  -7.52% (p=0.001 n=10)
AdjustTimers10000SingleThread-32     1.728m ± 6%   1.728m ± 5%       ~ (p=0.971 n=10)
AdjustTimers10000NoReset-32          263.0µ ± 3%   253.1µ ± 6%  -3.75% (p=0.023 n=10)
AdjustTimers10000NoSleep-32          306.8µ ± 5%   277.3µ ± 3%  -9.62% (p=0.000 n=10)
AdjustTimers10000NoResetNoSleep-32   245.3µ ± 3%   241.4µ ± 2%       ~ (p=0.529 n=10)

goos: darwin
goarch: arm64
pkg: time
cpu: Apple M3 Pro
                                   │ m3base.txt  │               m3.txt                │
                                   │   sec/op    │   sec/op     vs base                │
AdjustTimers10000-12                 385.5µ ± 3%   288.1µ ± 1%  -25.26% (p=0.000 n=10)
AdjustTimers10000SingleThread-12     1.213m ± 1%   1.195m ± 1%   -1.45% (p=0.001 n=10)
AdjustTimers10000NoReset-12          346.4µ ± 5%   280.8µ ± 1%  -18.94% (p=0.000 n=10)
AdjustTimers10000NoSleep-12          362.6µ ± 1%   292.5µ ± 1%  -19.33% (p=0.000 n=10)
AdjustTimers10000NoResetNoSleep-12   317.3µ ± 8%   279.8µ ± 2%  -11.79% (p=0.000 n=10)


Change-Id: Id3e10abfb1024f8e7883c8c366d941e4f1c2a894
Reviewed-on: https://go-review.googlesource.com/c/go/+/574738
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Russ Cox <rsc@golang.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/src/runtime/time.go b/src/runtime/time.go
index 7846542a80..96b7b76b07 100644
--- a/src/runtime/time.go
+++ b/src/runtime/time.go
@@ -607,15 +607,18 @@ func (t *timer) maybeAdd() {
 	t.lock()
 	t.trace("maybeAdd")
 	when := int64(0)
+	wake := false
 	if t.needsAdd() {
 		t.state |= timerHeaped
 		when = t.when
+		wakeTime := ts.wakeTime()
+		wake = wakeTime == 0 || when < wakeTime
 		ts.addHeap(t)
 	}
 	t.unlock()
 	ts.unlock()
 	releasem(mp)
-	if when > 0 {
+	if wake {
 		wakeNetPoller(when)
 	}
 }