runtime: add and use modtimer in netpoll

Currently when netpoll deadline is incrementally prolonged,
we delete and re-add timer each time.
Add modtimer function that does both and use it when we need
to modify an existing netpoll timer to avoid unnecessary lock/unlock.

TCP4OneShotTimeout-6  17.2µs ± 0%  17.0µs ± 0%  -0.82%  (p=0.008 n=5+5)
SetReadDeadline-6      274ns ± 2%   261ns ± 0%  -4.89%  (p=0.008 n=5+5)

Update #25729

Change-Id: I08b89dbbc1785dd180e967a37b0aa23b0c4613a8
Reviewed-on: https://go-review.googlesource.com/c/146339
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/netpoll.go

@@ -211,21 +211,13 @@ func poll_runtime_pollSetDeadline(pd *pollDesc, d int64, mode int) {
 		pd.wd = d
 	}
 	combo := pd.rd > 0 && pd.rd == pd.wd
-	// Reset current timers if necessary.
-	if pd.rt.f != nil && (pd.rd != rd0 || combo != combo0) {
-		pd.rseq++ // invalidate current timers
-		deltimer(&pd.rt)
-		pd.rt.f = nil
-	}
-	if pd.wt.f != nil && (pd.wd != wd0 || combo != combo0) {
-		pd.wseq++ // invalidate current timers
-		deltimer(&pd.wt)
-		pd.wt.f = nil
-	}
-	// Setup new timers.
+	rtf := netpollReadDeadline
 	if combo {
-		if pd.rt.f == nil {
-			pd.rt.f = netpollDeadline
+		rtf = netpollDeadline
+	}
+	if pd.rt.f == nil {
+		if pd.rd > 0 {
+			pd.rt.f = rtf
 			pd.rt.when = pd.rd
 			// Copy current seq into the timer arg.
 			// Timer func will check the seq against current descriptor seq,
@@ -234,21 +226,31 @@ func poll_runtime_pollSetDeadline(pd *pollDesc, d int64, mode int) {
 			pd.rt.seq = pd.rseq
 			addtimer(&pd.rt)
 		}
-	} else {
-		if pd.rd > 0 && pd.rt.f == nil {
-			pd.rt.f = netpollReadDeadline
-			pd.rt.when = pd.rd
-			pd.rt.arg = pd
-			pd.rt.seq = pd.rseq
-			addtimer(&pd.rt)
+	} else if pd.rd != rd0 || combo != combo0 {
+		pd.rseq++ // invalidate current timers
+		if pd.rd > 0 {
+			modtimer(&pd.rt, pd.rd, 0, rtf, pd, pd.rseq)
+		} else {
+			deltimer(&pd.rt)
+			pd.rt.f = nil
 		}
-		if pd.wd > 0 && pd.wt.f == nil {
+	}
+	if pd.wt.f == nil {
+		if pd.wd > 0 && !combo {
 			pd.wt.f = netpollWriteDeadline
 			pd.wt.when = pd.wd
 			pd.wt.arg = pd
 			pd.wt.seq = pd.wseq
 			addtimer(&pd.wt)
 		}
+	} else if pd.wd != wd0 || combo != combo0 {
+		pd.wseq++ // invalidate current timers
+		if pd.wd > 0 && !combo {
+			modtimer(&pd.wt, pd.wd, 0, netpollWriteDeadline, pd, pd.wseq)
+		} else {
+			deltimer(&pd.wt)
+			pd.wt.f = nil
+		}
 	}
 	// If we set the new deadline in the past, unblock currently pending IO if any.
 	var rg, wg *g

src/runtime/time.go

@@ -187,14 +187,22 @@ func deltimer(t *timer) bool {
 	tb := t.tb
 
 	lock(&tb.lock)
+	removed, ok := tb.deltimerLocked(t)
+	unlock(&tb.lock)
+	if !ok {
+		badTimer()
+	}
+	return removed
+}
+
+func (tb *timersBucket) deltimerLocked(t *timer) (removed, ok bool) {
 	// t may not be registered anymore and may have
 	// a bogus i (typically 0, if generated by Go).
 	// Verify it before proceeding.
 	i := t.i
 	last := len(tb.t) - 1
 	if i < 0 || i > last || tb.t[i] != t {
-		unlock(&tb.lock)
-		return false
+		return false, true
 	}
 	if i != last {
 		tb.t[i] = tb.t[last]
@@ -202,7 +210,7 @@ func deltimer(t *timer) bool {
 	}
 	tb.t[last] = nil
 	tb.t = tb.t[:last]
-	ok := true
+	ok = true
 	if i != last {
 		if !siftupTimer(tb.t, i) {
 			ok = false
@@ -211,11 +219,26 @@ func deltimer(t *timer) bool {
 			ok = false
 		}
 	}
+	return true, ok
+}
+
+func modtimer(t *timer, when, period int64, f func(interface{}, uintptr), arg interface{}, seq uintptr) {
+	tb := t.tb
+
+	lock(&tb.lock)
+	_, ok := tb.deltimerLocked(t)
+	if ok {
+		t.when = when
+		t.period = period
+		t.f = f
+		t.arg = arg
+		t.seq = seq
+		ok = tb.addtimerLocked(t)
+	}
 	unlock(&tb.lock)
 	if !ok {
 		badTimer()
 	}
-	return true
 }
 
 // Timerproc runs the time-driven events.