From 496ae8c84b2d3622bc767a727e3582e2b6bcffcd Mon Sep 17 00:00:00 2001 From: Kai Krakow Date: Sat, 13 May 2017 12:30:56 +0200 Subject: [PATCH] resolved: Recover from slow DNS responses When DNS is unreliable temporarily, the current implementation will never improve resend behavior again and switch DNS servers only late (current maximum timeout is 5 seconds). We can improve this by biasing the resend_timeout back to the current RTT when a successful response was received. Next time, a timeout is hit on this server, it will switch to the next server faster. Fixes: #5953 --- src/resolve/resolved-dns-server.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/src/resolve/resolved-dns-server.c b/src/resolve/resolved-dns-server.c index 63cb6a5bda6..9c3ee0136c6 100644 --- a/src/resolve/resolved-dns-server.c +++ b/src/resolve/resolved-dns-server.c @@ -304,7 +304,10 @@ void dns_server_packet_received(DnsServer *s, int protocol, DnsServerFeatureLeve if (s->max_rtt < rtt) { s->max_rtt = rtt; s->resend_timeout = CLAMP(s->max_rtt * 2, DNS_TIMEOUT_MIN_USEC, DNS_TIMEOUT_MAX_USEC); - } + } else if (s->resend_timeout > rtt) + /* If we received the packet faster than the resend_timeout, bias + * the resend_timeout back to the rtt. */ + s->resend_timeout = CLAMP((2 * s->resend_timeout + rtt) / 3, DNS_TIMEOUT_MIN_USEC, DNS_TIMEOUT_MAX_USEC); } void dns_server_packet_lost(DnsServer *s, int protocol, DnsServerFeatureLevel level, usec_t usec) {