runtime: use StorepNoWB instead of atomicstorep in netpoll

We only need the memory barrier from these stores,
and we only store nil over nil or over a static function value.
The write barrier is unnecessary.

name                  old time/op  new time/op  delta
TCP4OneShotTimeout-6  17.0µs ± 0%  17.0µs ± 0%  -0.43%  (p=0.032 n=5+5)
SetReadDeadline-6      205ns ± 1%   205ns ± 1%    ~     (p=0.683 n=5+5)

Update #25729

Change-Id: I66c097a1db7188697ddfc381f31acec053dfed2c
Reviewed-on: https://go-review.googlesource.com/c/146345
Run-TryBot: Dmitry Vyukov <dvyukov@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

diff --git a/src/runtime/netpoll.go b/src/runtime/netpoll.go
index 7e6e93d6c37f3711d4c5b942524e506781c51764..4f4abfcd2cb0213afe947c4a869f61748258612c 100644 (file)
--- a/src/runtime/netpoll.go
+++ b/src/runtime/netpoll.go
@@ -260,7 +260,7 @@ func poll_runtime_pollSetDeadline(pd *pollDesc, d int64, mode int) {
        // If we set the new deadline in the past, unblock currently pending IO if any.
        var rg, wg *g
        if pd.rd < 0 || pd.wd < 0 {
-               atomicstorep(unsafe.Pointer(&wg), nil) // full memory barrier between stores to rd/wd and load of rg/wg in netpollunblock
+               atomic.StorepNoWB(noescape(unsafe.Pointer(&wg)), nil) // full memory barrier between stores to rd/wd and load of rg/wg in netpollunblock
                if pd.rd < 0 {
                        rg = netpollunblock(pd, 'r', false)
                }
@@ -287,7 +287,7 @@ func poll_runtime_pollUnblock(pd *pollDesc) {
        pd.rseq++
        pd.wseq++
        var rg, wg *g
-       atomicstorep(unsafe.Pointer(&rg), nil) // full memory barrier between store to closing and read of rg/wg in netpollunblock
+       atomic.StorepNoWB(noescape(unsafe.Pointer(&rg)), nil) // full memory barrier between store to closing and read of rg/wg in netpollunblock
        rg = netpollunblock(pd, 'r', false)
        wg = netpollunblock(pd, 'w', false)
        if pd.rt.f != nil {
@@ -437,7 +437,7 @@ func netpolldeadlineimpl(pd *pollDesc, seq uintptr, read, write bool) {
                        throw("runtime: inconsistent read deadline")
                }
                pd.rd = -1
-               atomicstorep(unsafe.Pointer(&pd.rt.f), nil) // full memory barrier between store to rd and load of rg in netpollunblock
+               atomic.StorepNoWB(unsafe.Pointer(&pd.rt.f), nil) // full memory barrier between store to rd and load of rg in netpollunblock
                rg = netpollunblock(pd, 'r', false)
        }
        var wg *g
@@ -446,7 +446,7 @@ func netpolldeadlineimpl(pd *pollDesc, seq uintptr, read, write bool) {
                        throw("runtime: inconsistent write deadline")
                }
                pd.wd = -1
-               atomicstorep(unsafe.Pointer(&pd.wt.f), nil) // full memory barrier between store to wd and load of wg in netpollunblock
+               atomic.StorepNoWB(unsafe.Pointer(&pd.wt.f), nil) // full memory barrier between store to wd and load of wg in netpollunblock
                wg = netpollunblock(pd, 'w', false)
        }
        unlock(&pd.lock)