Re: [knot-dns-users] Debugging high CPU / Load - normal?

[daniel . salzman]

Hi Jonathan,

On 2020-09-22 23:11, Jonathan Hewlett wrote:
Hi,
We run around 50 knot servers around the world, with great success -
thanks for the software!

Thanks for this feedback :-)


We are just a little curious about seemingly high CPU usage, and how
best to interpret the results, if someone could advise?  Specifically,
we are seeing the majority of the cpu time in 'system' and not 'user',
what would that suggest is happening perhaps?

Could you provide me the output from `knotc status workers`?

I like htop. Are you able to send me a screenshot when running htop? :-)
[Don't forget to configure:
 F2
 Display options->Detailed CPU time 
(System/IO-Wait/Hard-IRQ/Soft-IRQ/Steal/Guest)
 F10
]

Best,
Daniel


Any tuning help gratefully received!

Our platform (sample)

24 Core CPU E5-2440 0 @ 2.40
64Gb RAM
SSD

knot-2.9.5, running on Centos 8.2

Currently receiving around 4k pps

Server is authoritative for a 278 zones, the largest zone file being
around 600Mb

Output of top

top - 20:50:38 up 6 days,  4:49,  2 users,  load average: 13.47,
12.34, 11.83
Tasks: 321 total,   2 running, 318 sleeping,   0 stopped,   1 zombie
%Cpu0  :  4.0 us, 34.1 sy,  0.0 ni, 60.3 id,  0.3 wa,  0.7 hi,  0.7
si,  0.0 st
%Cpu1  :  4.3 us, 19.4 sy,  0.0 ni, 75.3 id,  0.0 wa,  0.3 hi,  0.7
si,  0.0 st
%Cpu2  :  4.3 us, 33.8 sy,  0.0 ni, 60.9 id,  0.0 wa,  0.7 hi,  0.3
si,  0.0 st
%Cpu3  :  5.0 us, 21.2 sy,  0.0 ni, 73.2 id,  0.0 wa,  0.3 hi,  0.3
si,  0.0 st
%Cpu4  :  3.3 us, 34.9 sy,  0.0 ni, 61.5 id,  0.0 wa,  0.3 hi,  0.0
si,  0.0 st
%Cpu5  :  3.0 us, 20.2 sy,  0.0 ni, 76.2 id,  0.0 wa,  0.3 hi,  0.3
si,  0.0 st
%Cpu6  :  4.0 us, 35.2 sy,  0.0 ni, 60.4 id,  0.0 wa,  0.3 hi,  0.0
si,  0.0 st
%Cpu7  :  5.0 us, 18.7 sy,  0.0 ni, 76.0 id,  0.0 wa,  0.3 hi,  0.0
si,  0.0 st
%Cpu8  :  2.0 us, 35.0 sy,  0.0 ni, 62.3 id,  0.0 wa,  0.7 hi,  0.0
si,  0.0 st
%Cpu9  :  2.0 us, 20.0 sy,  0.0 ni, 77.7 id,  0.0 wa,  0.3 hi,  0.0
si,  0.0 st
%Cpu10 :  3.7 us, 34.4 sy,  0.0 ni, 61.2 id,  0.0 wa,  0.7 hi,  0.0
si,  0.0 st
%Cpu11 :  3.3 us, 20.7 sy,  0.0 ni, 75.7 id,  0.0 wa,  0.3 hi,  0.0
si,  0.0 st
%Cpu12 :  2.3 us, 34.6 sy,  0.0 ni, 62.1 id,  0.0 wa,  0.7 hi,  0.3
si,  0.0 st
%Cpu13 :  3.3 us, 20.7 sy,  0.0 ni, 75.7 id,  0.0 wa,  0.3 hi,  0.0
si,  0.0 st
%Cpu14 :  2.3 us, 33.6 sy,  0.0 ni, 59.7 id,  0.0 wa,  0.7 hi,  3.7
si,  0.0 st
%Cpu15 :  3.3 us, 19.7 sy,  0.0 ni, 76.3 id,  0.0 wa,  0.3 hi,  0.3
si,  0.0 st
%Cpu16 :  2.3 us, 34.0 sy,  0.0 ni, 58.7 id,  0.0 wa,  1.0 hi,  4.0
si,  0.0 st
%Cpu17 :  2.3 us, 21.5 sy,  0.0 ni, 75.8 id,  0.0 wa,  0.3 hi,  0.0
si,  0.0 st
%Cpu18 :  3.3 us, 34.8 sy,  0.0 ni, 57.2 id,  0.0 wa,  0.7 hi,  4.0
si,  0.0 st
%Cpu19 :  5.0 us, 19.3 sy,  0.0 ni, 75.1 id,  0.0 wa,  0.3 hi,  0.3
si,  0.0 st
%Cpu20 :  2.7 us, 35.3 sy,  0.0 ni, 60.0 id,  0.0 wa,  0.7 hi,  1.3
si,  0.0 st
%Cpu21 :  1.7 us, 20.5 sy,  0.0 ni, 77.2 id,  0.0 wa,  0.3 hi,  0.3
si,  0.0 st
%Cpu22 :  4.7 us, 32.4 sy,  0.0 ni, 58.5 id,  0.0 wa,  0.7 hi,  3.7
si,  0.0 st
%Cpu23 :  2.3 us, 19.0 sy,  0.0 ni, 78.3 id,  0.0 wa,  0.3 hi,  0.0
si,  0.0 st
MiB Mem :  64107.4 total,  46764.9 free,  11733.6 used,   5608.8
buff/cache
MiB Swap:  32248.0 total,  32248.0 free,      0.0 used.  51670.0 avail
Mem

PID USER      PR   NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+
COMMAND
213370 knot  20   0      34.0g   9.6g  41784 S 644.9  15.3   1319:12
/usr/sbin/knotd

Thanks again for this great product.

Jonathan
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