[dnsdist] dnsdist 1.7.4 Debian Bullseye vs 1.8.4 Bullseye

Remi Gacogne remi.gacogne at powerdns.com
Mon Oct 2 11:53:31 UTC 2023

Hi Ales,

On 25/09/2023 16:09, Aleš Rygl via dnsdist wrote:
>>     I would to kindly ask for help or and advice. I have just upgraded 
>> one of our dnsdist instances from 1.7.4 do 1.8.4 together with OS 
>> upgrade (Debian 11.7 to 12.1). Everything works fine, no issues 
>> observed apart some deprecated config references. What is a big 
>> surprise to me is CPU usage. The newer version has nearly two times 
>> higher CPU consumption in userspace. I am nearly at 80% CPU with 16 
>> physical cores (was about 40%). We have a lot of TLS (DoT) sessions 
>> (30k) and 60kqps in total (30k via DoT) here. The latency measured by 
>> dnsdist went up also. We are collecting all the metrics dnsdist 
>> produces via graphite so I can check counters, what could be wrong.

Wow, that's awful. It's the first time I hear about such a regression, 
and I really would like to understand what is going on.
1/ Are you using our packages, compiling yourself, or perhaps using the 
Debian ones?
2/ Do you think it would be possible for you to try downgrading the 
instance to 1.7.4 on Debian 12.1? It might help us pinpointing whether 
the issue is related to a system change (I have seen people complain 
about the performance of OpenSSL 3.0.x compared to 1.1.1x, for example).
3/ Would you mind sharing your configuration?
4/ And finally, do you think it would be possible for you to collect a 
perf trace on this instance? It would require installing linux-perf, if 
possible the debug symbols for dnsdist (dnsdist-dbgsym) then running 
'perf record --call-graph dwarf -p <pid of running dnsdist process> -o 
</path/to/output/file>' for a few dozens of seconds to collect a trace, 
stopping it with Ctrl+C and finally getting a report with "perf report 
-i </path/to/previous/file> --stdio". It should tell us where the CPU 
usage is going.

Best regards,
Remi Gacogne
PowerDNS.COM BV - https://www.powerdns.com/
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