daemon: set TCP_DEFER_ACCEPT on everything but NNTP

This Linux-specific option can save us some wakeups during
the TLS negotiation phase, and it can help with ordinary HTTP,
too.

Plain NNTP (and in the future, POP3) are the only things which
require the server send messages, first.

1 files changed, 22 insertions, 4 deletions

diff --git a/lib/PublicInbox/Daemon.pm b/lib/PublicInbox/Daemon.pm
index c4481555..8b59b65f 100644
--- a/lib/PublicInbox/Daemon.pm
+++ b/lib/PublicInbox/Daemon.pm
@@ -8,6 +8,7 @@ use warnings;
 use Getopt::Long qw/:config gnu_getopt no_ignore_case auto_abbrev/;
 use IO::Handle;
 use IO::Socket;
+use Socket qw(IPPROTO_TCP);
 use Cwd qw/abs_path/;
 STDOUT->autoflush(1);
 STDERR->autoflush(1);
@@ -552,6 +553,18 @@ sub tls_start_cb ($$) {
         }
 }
 
+sub defer_accept ($) {
+        if ($^O eq 'linux') {
+                my ($s) = @_;
+                my $x = getsockopt($s, IPPROTO_TCP, Socket::TCP_DEFER_ACCEPT());
+                return unless defined $x; # may be Unix socket
+                my $sec = unpack('i', $x);
+                return if $sec > 0; # systemd users may set a higher value
+                setsockopt($s, IPPROTO_TCP, Socket::TCP_DEFER_ACCEPT(), 1);
+        }
+        # TODO FreeBSD accf_http / accf_data
+}
+
 sub daemon_loop ($$$) {
         my ($refresh, $post_accept, $nntpd) = @_;
         PublicInbox::EvCleanup::enable(); # early for $refresh
@@ -581,10 +594,15 @@ sub daemon_loop ($$$) {
         $SIG{HUP} = $refresh;
         $SIG{CHLD} = 'DEFAULT';
         $SIG{$_} = 'IGNORE' for qw(USR2 TTIN TTOU WINCH);
-        # this calls epoll_create:
-        @listeners = map {
-                PublicInbox::Listener->new($_,
-                                $post_accept{sockname($_)} || $post_accept)
+        @listeners = map {;
+                my $tls_cb = $post_accept{sockname($_)};
+
+                # NNTPS, HTTPS, HTTP, and POP3S are client-first traffic
+                # NNTP and POP3 are server-first
+                defer_accept($_) if $tls_cb || !$nntpd;
+
+                # this calls epoll_create:
+                PublicInbox::Listener->new($_, $tls_cb || $post_accept)
         } @listeners;
         PublicInbox::DS->EventLoop;
         $parent_pipe = undef;