15 Srp
2016
15 Srp
'16
19:27
Hey Matthijs,
On 15 August 2016 at 06:32, Matthijs Mekking <matthijs(a)pletterpet.nl> wrote:
Hi Jan,
Thanks for your response. Some comments inline:
On 15-08-16 14:29, Jan Včelák wrote:
Even if it's nearby, it's the latency that kills it. I think the number of
workers in Knot is ~ number of cores ~ number of proxied requests
in-flight. Resolvers, proxies and LBs use coroutines, event loops or
pipelines to resolve queries asynchronously, so they are able to have three
orders of magnitude more requests in-flight. There was someone working on
reimplementing the proxy module with per-worker libuv loops a few months
ago, I don't know what's the status now, but that would help a lot.
Hi Matthijs,
processing of queries in Knot DNS is synchronous. So the UDP thread is
blocked until the query processing is finished. This usually doesn't
matter for authoritative server because the server can construct the
response immediately.
For dnsproxy, this is a problem. The dnsproxy module establishes a TCP
connection to the resolver and waits for the answer. During that time
the UDP handler thread is just idling.
The dnsproxy AFAICS will use the same transport protocol as the incoming
query. In our tests this is all UDP. So I don't think any TCP connection is
established.
Also, the query is forwarded to an authoritative server nearby, not a
resolver, which should be a lot faster. There is still idle time of course,
and perhaps too much.
I'm affraid this couldn't be fixed easily without deep changes in the
Perhaps you can try increasing the worker count to something like 100? It
should help. Honestly, if you're looking for public-facing DNS proxy with
filtering and decent performance, you'll be better served by something
else. RRL (or rate limits for uncached responses) is relatively easy to
implement in DNS firewall in Knot Resolver (have a look at the 1.1 release
post) compared to reimplementing the DNS proxy module in authoritative.
Marek
knotd architecture.
Anyway, we are interested in your discoveries.
Me too.
Best regards,
Matthijs Cheers,
Jan
On 15.8.2016 14:12, Matthijs Mekking wrote:
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Hi,
I recently tested the mod-dnsproxy performance and I am disappointed in
the results:
Knot in our test setup can do ~320K QPS.
When using our own proxy in front of knot, we achieve quite a
performance hit, only able to do ~120K QPS.
However, when configuring knot to use the mod-dnsproxy, the performance
drops to ~7K QPS.
I am planning to investigate what causes this significant drop, but if
you have any insights or other measurements already I would love to hear
about them.
Best regards,
Matthijs
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