From: Štěpán Balážik <stepan.balazik@nic.cz>
Date: Tue, 8 Sep 2020 09:51:25 +0000 (+0200)
Subject: selection: limit backing of the timeout
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8f51f4979b23905e1a587ae8d49de74cfa105d23;p=thirdparty%2Fknot-resolver.git

selection: limit backing of the timeout
---

diff --git a/lib/selection.c b/lib/selection.c
index fe4322339..8fe967e4b 100644
--- a/lib/selection.c
+++ b/lib/selection.c
@@ -38,6 +38,7 @@ void *prefix_key(const uint8_t *ip, size_t len) {
 
 #define DEFAULT_TIMEOUT 400
 #define MAX_TIMEOUT 10000
+#define MAX_BACKOFF 5
 
 const struct rtt_state default_rtt_state = {0, DEFAULT_TIMEOUT/4, 0};
 
@@ -108,14 +109,21 @@ bool no_rtt_info(struct rtt_state s) {
 
 #define MINIMAL_TIMEOUT_ADDITION 20
 
-// This is verbatim (minus the default timeout value and minimal variance) RFC2988, sec. 2
-int32_t calc_timeout(struct rtt_state state) {
-	int32_t timeout = state.srtt + MAX(4 * state.variance, MINIMAL_TIMEOUT_ADDITION);
-	timeout = timeout * (1 << state.consecutive_timeouts);
-	if (timeout > MAX_TIMEOUT) {
+unsigned back_off_timeout(uint32_t to, int pow) {
+	if (pow > MAX_BACKOFF) {
+		return to *= 1 << MAX_BACKOFF;
+	} else {
+		return to * (1 << pow);
+	}
+	if (to > MAX_TIMEOUT) {
 		return MAX_TIMEOUT;
 	}
-	return timeout;
+}
+
+// This is verbatim (minus the default timeout value and minimal variance) RFC2988, sec. 2
+unsigned calc_timeout(struct rtt_state state) {
+	int32_t timeout = state.srtt + MAX(4 * state.variance, MINIMAL_TIMEOUT_ADDITION);
+	return back_off_timeout(timeout, state.consecutive_timeouts);
 }
 
 // This is verbatim RFC2988, sec. 2
@@ -219,7 +227,7 @@ struct kr_transport *choose_transport(struct choice choices[],
 	unsigned timeout = calc_timeout(choices[choice].address_state->rtt_state);
 	if (no_rtt_info(choices[choice].address_state->rtt_state)) {
 		// Exponential back-off when retrying after timeout and choosing an unknown server
-		timeout *= 1 << timeouts;
+		timeout = back_off_timeout(timeout, timeouts);
 	}
 
 	enum kr_transport_protocol protocol;
diff --git a/lib/selection_iter.c b/lib/selection_iter.c
index f54c333ab..5b2cb3c94 100644
--- a/lib/selection_iter.c
+++ b/lib/selection_iter.c
@@ -202,7 +202,7 @@ void iter_choose_transport(struct kr_query *qry, struct kr_transport **transport
 			const char *ns_str = kr_straddr(&(*transport)->address.ip);
 			if ((*transport)->protocol) {
 				VERBOSE_MSG(qry,
-				"=> id: '%05u' choosing: '%s'@'%s' with timeout %d ms zone cut: '%s'\n",
+				"=> id: '%05u' choosing: '%s'@'%s' with timeout %u ms zone cut: '%s'\n",
 				qry->id, ns_name, ns_str ? ns_str : "", (*transport)->timeout, zonecut_str);
 			} else {
 				VERBOSE_MSG(qry,