internal/poll: don't queue port completion entry for udp on windows

This CL sets the FILE_SKIP_COMPLETION_PORT_ON_SUCCESS notification mode
for all udp and tcp networks.

When SetFileCompletionNotificationModes was implemented, back in
go 1.2 [1], it was not possible to enable this mode on udp connections
because it is buggy on Windows 7 and earlier. The bug was fixed on
Windows 8. We can safely enable this mode now, since go 1.21
will require Windows 10 or higher.

While here, I noticed that this mode is only enabled for tcp, but not
for tcp4 nor tcp6. I don't think this restriction makes sense, so I'm
lifting it.

The performance gains are relevant:

name                           old time/op    new time/op    delta
ReadWriteMsgUDPAddrPort-12       13.3µs ± 4%    11.2µs ± 8%  -15.90%  (p=0.000 n=10+9)
WriteToReadFromUDP-12            14.5µs ±18%    11.4µs ± 4%  -21.35%  (p=0.000 n=10+9)
WriteToReadFromUDPAddrPort-12    13.4µs ± 3%    11.0µs ± 2%  -18.00%  (p=0.000 n=10+9)

[1] https://codereview.appspot.com/12409044

Change-Id: Idf41c35898beceac39d21decb47910f7d8ac247b
Reviewed-on: https://go-review.googlesource.com/c/go/+/463839
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Run-TryBot: Quim Muntal <quimmuntal@gmail.com>
Reviewed-by: Bryan Mills <bcmills@google.com>

diff --git a/src/internal/poll/fd_windows.go b/src/internal/poll/fd_windows.go
index 3a4a74f2aeb559e96e4360cb8afaefc2146cbfa4..f863ecb99829b776c1788c2126e44579409e92f7 100644 (file)
--- a/src/internal/poll/fd_windows.go
+++ b/src/internal/poll/fd_windows.go
@@ -325,9 +325,9 @@ func (fd *FD) Init(net string, pollable bool) (string, error) {
        if pollable && useSetFileCompletionNotificationModes {
                // We do not use events, so we can skip them always.
                flags := uint8(syscall.FILE_SKIP_SET_EVENT_ON_HANDLE)
-               // It's not safe to skip completion notifications for UDP:
-               // https://docs.microsoft.com/en-us/archive/blogs/winserverperformance/designing-applications-for-high-performance-part-iii
-               if net == "tcp" {
+               switch net {
+               case "tcp", "tcp4", "tcp6",
+                       "udp", "udp4", "udp6":
                        flags |= syscall.FILE_SKIP_COMPLETION_PORT_ON_SUCCESS
                }
                err := syscall.SetFileCompletionNotificationModes(fd.Sysfd, flags)