From: Michael Pratt <mpratt@google.com>
Date: Thu, 29 Oct 2020 20:03:57 +0000 (-0400)
Subject: runtime: elide timer re-check if P has no timers
X-Git-Tag: go1.16beta1~381
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=89a6540d8a93b95620080a8145c9882b063e3e46;p=gostls13.git

runtime: elide timer re-check if P has no timers

In golang.org/cl/264477, I missed this new block after rebasing past
golang.org/cl/232298. These fields must be zero if there are no timers.

Updates #28808
Updates #18237

Change-Id: I2d9e1cbf326497c833daa26b11aed9a1e12c2270
Reviewed-on: https://go-review.googlesource.com/c/go/+/266367
Run-TryBot: Michael Pratt <mpratt@google.com>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Michael Pratt <mpratt@google.com>
---

diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index ced27ceb3a..071257b5a5 100644
--- a/src/runtime/proc.go
+++ b/src/runtime/proc.go
@@ -2606,9 +2606,10 @@ stop:
 	// safe-points. We don't need to snapshot the contents because
 	// everything up to cap(allp) is immutable.
 	allpSnapshot := allp
-	// Also snapshot idlepMask. Value changes are OK, but we can't allow
+	// Also snapshot masks. Value changes are OK, but we can't allow
 	// len to change out from under us.
 	idlepMaskSnapshot := idlepMask
+	timerpMaskSnapshot := timerpMask
 
 	// return P and block
 	lock(&sched.lock)
@@ -2670,10 +2671,12 @@ stop:
 	// transitioning from spinning to non-spinning. Note that we cannot use
 	// 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 {
-		w := nobarrierWakeTime(_p_)
-		if w != 0 && (pollUntil == 0 || w < pollUntil) {
-			pollUntil = w
+	for id, _p_ := range allpSnapshot {
+		if timerpMaskSnapshot.read(uint32(id)) {
+			w := nobarrierWakeTime(_p_)
+			if w != 0 && (pollUntil == 0 || w < pollUntil) {
+				pollUntil = w
+			}
 		}
 	}
 	if pollUntil != 0 {