From a9280fa2de5b9dc13f75dd3aebdf4a218fca451e Mon Sep 17 00:00:00 2001
From: Dmitry Vyukov <dvyukov@google.com>
Date: Wed, 31 Oct 2018 11:31:31 +0100
Subject: [PATCH] runtime: don't wake timeproc needlessly
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It's not always necessary to wake timerproc even if we add
a new timer to the top of the heap. Since we don't wake and
reset timerproc when we remove timers, it still can be sleeping
with shorter timeout. It such case it's more profitable to let it
sleep and then update timeout when it wakes on its own rather than
proactively wake it, let it update timeout and go to sleep again.

name                  old time/op  new time/op  delta
TCP4OneShotTimeout-6  18.6µs ± 1%  17.2µs ± 0%   -7.66%  (p=0.008 n=5+5)
SetReadDeadline-6      562ns ± 5%   319ns ± 1%  -43.27%  (p=0.008 n=5+5)

Update #25729

Change-Id: Iec8eacb8563dbc574a82358b3bac7ac479c16826
Reviewed-on: https://go-review.googlesource.com/c/146337
Reviewed-by: Ian Lance Taylor <iant@golang.org>
---
 src/net/tcpsock_test.go | 31 +++++++++++++++++++++++++++++++
 src/runtime/time.go     | 10 +++++-----
 2 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/src/net/tcpsock_test.go b/src/net/tcpsock_test.go
index c2f26b1770..36d2ccb09a 100644
--- a/src/net/tcpsock_test.go
+++ b/src/net/tcpsock_test.go
@@ -796,3 +796,34 @@ func TestCopyPipeIntoTCP(t *testing.T) {
 		t.Fatal(err)
 	}
 }
+
+func BenchmarkSetReadDeadline(b *testing.B) {
+	ln, err := newLocalListener("tcp")
+	if err != nil {
+		b.Fatal(err)
+	}
+	defer ln.Close()
+	var serv Conn
+	done := make(chan error)
+	go func() {
+		var err error
+		serv, err = ln.Accept()
+		done <- err
+	}()
+	c, err := Dial("tcp", ln.Addr().String())
+	if err != nil {
+		b.Fatal(err)
+	}
+	defer c.Close()
+	if err := <-done; err != nil {
+		b.Fatal(err)
+	}
+	defer serv.Close()
+	c.SetWriteDeadline(time.Now().Add(2 * time.Hour))
+	deadline := time.Now().Add(time.Hour)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		c.SetReadDeadline(deadline)
+		deadline = deadline.Add(1)
+	}
+}
diff --git a/src/runtime/time.go b/src/runtime/time.go
index 790819f259..5e1a925dee 100644
--- a/src/runtime/time.go
+++ b/src/runtime/time.go
@@ -156,7 +156,7 @@ func (tb *timersBucket) addtimerLocked(t *timer) bool {
 	}
 	if t.i == 0 {
 		// siftup moved to top: new earliest deadline.
-		if tb.sleeping {
+		if tb.sleeping && tb.sleepUntil > t.when {
 			tb.sleeping = false
 			notewakeup(&tb.waitnote)
 		}
@@ -164,10 +164,10 @@ func (tb *timersBucket) addtimerLocked(t *timer) bool {
 			tb.rescheduling = false
 			goready(tb.gp, 0)
 		}
-	}
-	if !tb.created {
-		tb.created = true
-		go timerproc(tb)
+		if !tb.created {
+			tb.created = true
+			go timerproc(tb)
+		}
 	}
 	return true
 }
-- 
2.50.0