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resolved: Recover from slow DNS responses

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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
This commit is contained in:
Kai Krakow 2017-05-13 12:30:56 +02:00 committed by Lennart Poettering
parent 9af868392b
commit 496ae8c84b
1 changed files with 4 additions and 1 deletions
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5
src/resolve/resolved-dns-server.c
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@ -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) {