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There always is a lot of talk about Mikrotik RouterOS CPU usage. I wanted to take a few minutes and go over a real-world example and explain some of the ins and outs when discussing Mikrotik CPU usage.

Let’s talk about the router in question. This is a CCR1016-12s-1S+. This is a 16 core 1.2GHz per core and 2GB RAM tilex based router. It is currently pulling in 1,764,849 IPv4 routes. There are two transit provider BGP feeds, multiple direct peers, an Internet Exchange peer to dual-route servers. The router handles a little over 3 gigs of routed traffic at peak times. Most of the traffic is on VLANs coming from a Cisco switch to the SFPPlus port.

One of the first things people turn on is the overall CPU usage within winbox. I like to think of this as an overall view of the CPUs on this router. Keep in mind there are 16.

Th next thing to investigate when it comes to CPU is to open up System..resources. Once there clock on CPU.

It will then bring up a screen that looks like the following.

Oh My we have 100% CPU! Must replace this router ASAP! Calm down, remember you have 16 cores. So, why is this CPU at 100% and what ramifications does this have?

Remember earlier when we talked about BGP? In Mikrotik, BGP is not a multi-core aware process. This means BGP is limited to just one core to do it’s work. Since there are always routes being withdrawn and re-added to the routing table it is a busy process. Lots of math calculations going on. The key thing is this is expected behavior on a router running multiple BGP peers such as this one. This is not a bad thing, but not ideal. Throwing more cores at BGP is not the answer. Optimizing the process, as it has been done in V7 is the way to go.

If we expand the CPU window we will notice other processes are multi-core aware and.or are spreading their load among different cores.

As you can see we are in pretty good shape. We have a few CPUs above 50% utilization but, only a few. I will keep reminding you of the fact we have 16 of them.

Closing notes:
Diagnosing CPU issues can get a little complicated because routers like the 3011 have some have the majority of their ports shared with a single CPU bus.  https://wiki.mikrotik.com/images/f/f3/Switch_chip_block_diagram.png. As you can tell in the diagram there are 5 ports which share 1 Gig to the CPU.  The fact that an actual switch chip with hardware offloading is in the middle helps, but the bus is still oversold.  This is one reason consolidating routers to an actual switch will make a difference.  

Janis Megis from Mikrotik had presentation at MUM, which is a little older now, still sheds a lot of light on how Mikrotik CPU works.  https://mum.mikrotik.com/presentations/US10/Megis.pdf There is some pretty interesting stuff starting on page 14

With Mikrotik switching to ARM processors we will see huge differences with them and RotuerOS7. We will see less cores, but better utilization of those cores. The new 2004 with all SFP and 2 25 gig ports only has 4 CPU.

So the next time you look at a router, take a few moments to see how utilized the entire CPU architecture is instead of just one CPU.

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