[dnsdist] dnsdist 1.7.4 Debian Bullseye vs 1.8.4 Bullseye

Remi Gacogne remi.gacogne at powerdns.com
Thu Oct 5 09:38:27 UTC 2023


On 05/10/2023 10:41, Aleš Rygl via dnsdist wrote:
>      Thanks for your response. After some deep documentation reading and 
> config tweaking I am nearly on the previous values regarding CPU load, 
> apart from latency, which is still higher (1.3ms -> 2.3ms). I suspect a 
> different way the latency is likely computed (I noticed a new set of 
> latency counters for TLS, TCP, etc.) here.  The key configuration 
> parameter is setMaxTCPClientThreads(). Changing anything else (cache 
> shards, number of listeners, etc.) has nearly no impact. We had 256 with 
> 1.7.4. now it is 16. Going up here means a rapid increase of CPU load, 
> having less than 16 means dropping TCP connections in showTCPStats(), 
> where Queued hits Max Queued. Insane values like 1024 kills the CPU. We 
> have a physical server with 16 phys. cores, OS sees 32 cores.

OK, this is clearly unexpected. I mean, since 1.4.0 you should not be 
needing more TCP worker threads than the number of cores, since a single 
worker can handle a lot (easily thousands) of TCP connections, but 
having a larger value should not kill the CPU so I'm wondering if we are 
busy-looping somewhere. I have not been able to reproduce that so far, 
so I would be really interested in seeing the perf output if you can get 

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

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