Is SQM needed when the WAN link is not saturated?

RouterOS
1

I was not able to answer this question looking at the internet, and LLMs tend to just agree with whatever I write.

Let me go straight to the point. Is SQM needed at all when the link is not saturated? Because from my understanding on how SQMs works is that their job is to control latency when the link is saturated, but, if there is no saturation, then it can even add more latency, not much, but still some latency, because it would bypass the fasttrack that could handle the packets directly at hardware.

I don’t really care much about throughput. 1gbps, my current wan connection, is plenty and I don’t have any desire to upgrade it, but I really do care about latency, and I would like to have the lowest latency possible.

I still need to perform a few tests with SQM on my RB5009. But I think the CPU will not be fast enough to do it. If you’ve done it, can you share your experience and the throughput that it was able to process?

2

If your connection isn't saturated then you don't need sqm.

If you apply sqm to an unsaturated link, it will not buffer packets needlessly and there will be no additional delay in forwarding.

Fasttrack is still done in software. It uses specific hardware support when it's available (and on the rb5009 it is) but it is still fundamentally software driven. In these scenarios the delay is set by irq and scheduling latency. This will not be materially affected by your choice of queue.

The rb5009 easily does 1 Gbps with sqms.

EDIT: Lock your device cpu frequency to the max value (1400MHz). The device-mode feature will fight you on this. You may believe that the device won't be able to handle your load because you're looking at your cpu usage at 350MHz. (The system->resources panel shows you the current actual cpu freq.)