TP-Link Archer C7 v2 5 GHz latency

Hi folks, I'm trying to evaluate a latency issue I'm seeing with my home network on the 5 GHz Wi-Fi band.

I'm running a TP-Link Archer C7 v2 Wi-Fi router on OpenWrt 23.05.0 r23497-6637af95aa. The router has the 5 GHz Qualcomm Atheros QCA9880 802.11ac/n radio enabled on channel 153 at 80 MHz channel width and 30 dBm maximum transmit power, and the 2.4 GHz Qualcomm Atheros QCA9550 802.11b/g/n radio enabled on channel 11 at 20 MHz channel width and 24 dBm maximum transmit power.

The upstream connection is a cable modem providing internet speeds of ~235Mbps download and ~12Mbps upload, so my expectations of internet throughput are realistic. I realize that the 80 MHz channel width on the 5 GHz band won't benefit my internet throughput, considering it's capped at 235/12, but a) it at least allows LAN traffic to pass at a higher throughput, and b) the issues I'm seeing happen regardless of the 5 GHz channel width (20/40/80 are my options).

I monitor latency on my network using collectd to send pings from various hosts on my network to other hosts (both wifi and wired) on the LAN, as well as hosts on the internet. I also test throughput using speedtest-cli on various hosts, although throughput is less of a concern (see the cable modem limiting note earlier).

In general, what I see is slightly higher latency/lower drop rate on the 2.4 GHz network, and lower latency/higher drop rate on the 5 GHz network. This generally results in the 5 GHz network delivering content faster than the 2.4 GHz network, which is sort of expected, but being a bit more sporadic in its responses than the 2.4 GHz network, which is what puzzles me. In other words, the 5 GHz network delivers content faster IF it responds... but it doesn't always respond reliably. This mostly shows itself with SSH terminal sessions to hosts on the LAN/WAN being laggy, and websites taking a bit longer to respond to initial requests.

Our house is a big old building with lots of plaster walls, multiple floors, and several brick chimneys, with Wi-Fi use spread out all over the place, so there is an element of transmission issues, which 2.4 GHz is more capable of overcoming than 5 GHz. However, these test results hold up even in the next room over on the same floor of the router, so I'm not entirely sure it's to blame.

My question is, is this simply a fact of life of 5 GHz Wi-Fi, or is it an issue with this device, or could there be something else I'm missing?

Not really, that is hard (and slightly beyond) the limit of what an archer c7 can do, routing alone - but you're expecting full speed for the wireless on top, using a single core which is really a bit too much. In these situations the latencies suffer first, you'll quickly start to see sawtooth like throughputs.

The single CPU seems to be handling things ok, at least according to collectd. Idle is rarely below 60%. Here's the cpu breakdown over the past 7 days:

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Anyone have any other thoughts? If there's more diagnostic information or metrics I could provide, let me know.