[PATCH 2/2] send_cmd: throttle `sleeping on sendmsg' messages

[Eric Wong <e@80x24.org>]

Emitting a message every 100ms was too much for busy machines.
Throttle it to 1.6s to avoid flooding user terminals by emitting
every 16 sleeps.  A power-of-two (16) was chosen for its
optimization potential via bitwise AND.  Since perl(1) doesn't
do this optimization, we open code the bitwise AND.  I don't
assume an optimizing compiler for Inline::C, either, since I
find working in C far more enjoyable with optimizations off.
---
 lib/PublicInbox/CmdIPC4.pm | 3 ++-
 lib/PublicInbox/Spawn.pm   | 6 ++++--
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/lib/PublicInbox/CmdIPC4.pm b/lib/PublicInbox/CmdIPC4.pm
index bdf17a3f..af49f36d 100644
--- a/lib/PublicInbox/CmdIPC4.pm
+++ b/lib/PublicInbox/CmdIPC4.pm
@@ -12,7 +12,8 @@ sub sendmsg_retry ($) {
 	return 1 if $!{EINTR};
 	return unless ($!{ENOMEM} || $!{ENOBUFS} || $!{ETOOMANYREFS});
 	return if $_[0]-- == 0;
-	warn "# sleeping on sendmsg: $! ($_[0] tries left)\n";
+	# n.b. `N & (power-of-two - 1)' is a faster `N % power-of-two'
+	warn "# sleeping on sendmsg: $! ($_[0] tries left)\n" if !($_[0] & 15);
 	select(undef, undef, undef, 0.1);
 	1;
 }
diff --git a/lib/PublicInbox/Spawn.pm b/lib/PublicInbox/Spawn.pm
index 1c6cc5be..d818af0f 100644
--- a/lib/PublicInbox/Spawn.pm
+++ b/lib/PublicInbox/Spawn.pm
@@ -184,8 +184,10 @@ static int sendmsg_retry(long *tries)
 	case EINTR: PERL_ASYNC_CHECK(); return 1;
 	case ENOBUFS: case ENOMEM: case ETOOMANYREFS:
 		if (*tries-- == 0) return 0;
-		fprintf(stderr, "# sleeping on sendmsg: %s (%ld tries left)\n",
-			strerror(err), *tries);
+		if (!(*tries & 15))
+			fprintf(stderr,
+				"# sleeping on sendmsg: %s (%ld tries left)\n",
+				strerror(err), *tries);
 		nanosleep(&req, NULL);
 		PERL_ASYNC_CHECK();
 		return 1;