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kraal
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RBD52G-5HacD2HnD: cores not used evenly under load ?

Wed Apr 27, 2022 2:11 pm

Hello,

I sarted using yesterday a spare hAP AC2 as a "router on a stick" and I'm encountering some issues when running iperf3.
The device (RBD52G-5HacD2HnD) is running under routerOS 6.49.6 (stable) and takes care of the routing (inter-VLAN) between 2 switches, an accesspoint and the WAN port.
I'm running the following test:

  • AC2 takes care of the routing / firewall rules
  • iperf3 server is on VLAN-AAA
  • iperf3 client is on VLAN-BBB
  • iperf3 server is run on a device connected to switch1 which in turn is connected (via trunk port) to ether3 of the AC2
  • iperf3 client is run on a device connected to switch2 which in turn is connected (via trunk port) to ether2 of the AC2
  • iperf3 commands that are run on the client: "iperf3 -c <server_ip> -P 30 -p 5201 -bg -t 30 -4" and "iperf3 -c <server_ip> -P 30 -p 5201 -bg -t 30 -4 -R"

When running these tests, I observe three things:

  • the load on the AC2 is not shared among the 4 cores (1 core is at 100%, 2 cores are at 0%, the last core is somewhere between 2% and 15%).
  • CPU0 and CPU2 are rarely above 2% usage (i.e. CPU1 or CPU3 go to 100%), they are almost unused...
  • the maximum throughput I get (inter-VLAN) is ~370 Mbps (while all links are 1Gbps full duplex, cables are tested)

I guess that the fact that the cores are not used evenly may cause this bottleneck/performance issue. Can anybody confirm that this may cause this issue ? (or should I look elsewhere)

Thank you for your help!

Note 1: there is no hardware offloading on the AC2
Note 2: wireless is disabled on the device
Note 3: there are ~10 VLANs
Note 4: rules-wise there are: 4 NAT rules, 3 RAW rules, 0 Mangle, fasttrack is activated, the "allow iPerf traffic" rule is the 9th rule in the forward chain (total of 159 rules including input, output and forwards for all VLANs)
Note 5: on the switches the CPU load is max 4% when running the tests
Note 6: when staying on the same switch, with the same test command, the throughput is ~960Mbps
Note 7: The "CPU usage issue" is very similar to this one, but with ahAP AC2 instead of a RB450Gx4: viewtopic.php?hilit=CPU&p=924912&sid=3d ... ce850ddd7f however the latest stable routerOS v6 does not fixes it for the AC2
 
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Znevna
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Re: RBD52G-5HacD2HnD: cores not used evenly under load ?

Wed Apr 27, 2022 2:31 pm

+all IPv6 traffic is processed by the 4th core.
 
kraal
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Re: RBD52G-5HacD2HnD: cores not used evenly under load ?

Wed Apr 27, 2022 2:55 pm

+all IPv6 traffic is processed by the 4th core.
There is no IPv6 traffic in my case. Do you mean that 1 core won't be used at all because it is dedicated to IPv6 ?
 
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Znevna
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Re: RBD52G-5HacD2HnD: cores not used evenly under load ?

Wed Apr 27, 2022 2:56 pm

Nope, just stating other bugs with ac2.
 
kraal
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Re: RBD52G-5HacD2HnD: cores not used evenly under load ?

Fri May 06, 2022 3:54 pm

Update: I received the following answer from Mikrotik's support:

There are processes that cannot be split to multiple CPUs, in these cases you may see CPU usage as yours, this is expected and that is by design. We constantly improving CPU utilization algorithms, please keep the device up to date.
 
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chechito
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Re: RBD52G-5HacD2HnD: cores not used evenly under load ?

Fri May 06, 2022 5:38 pm

i think , if your workload get one core of hap-ac2 close to 100% you may consider upgrading to rb4011igs+rm

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