Need help explaining Crusader plots

[richb-hanover]

@Zoxc @dtaht - I have a bunch of questions about what Crusader plots actually show, and how to explain lousy tests.

This is a first cut for a possible page for the Crusader repo. I would love to get your comments on the following - I'll keep tweaking up this article until it's "good enough". Thanks.

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Comparison of Crusader Plots

A Crusader test packs a lot of data into a simple display. Here's how to understand what it's showing:

Over Ethernet

This is a plot of a pretty good test. It was performed between two devices on Ethernet - an M2 Mac mini running Crusader GUI connected to a Crusader Server running on a Raspberry Pi 4. Here is what it shows:

• The Download and Upload traces (green and blue, respectively) show throughput of nearly 1,000 mbps (1 Gbps), the rated values for the device interfaces.
• The Combined plot shows transfers in both directions (green and blue) running at nearly their full rate. The purple trace is the sum of both.
• The Download latency is a bit spiky, with most values ranging between 5 and 25 msec. (Can anyone say why?)
• The Upload latency is quite low: well under 5 msec.
• The Combined latency plot (purple) shows the sum of the latency in each direction (green, blue).
• There appears to be a single packet dropped around 13.2 seconds in the bottom plot.

Over Wi-Fi from Living Room

This is a mess. That is, the Crusader test shows my Wi-Fi network is a wreck.

It's a test run from an Intel MacBook with Crusader GUI over Wi-Fi, tested against the same Raspberry Pi4 running the server. (My router is a Belkin RT3200 with OpenWrt 22.03.5. I am currently afraid to upgrade to 23.05.4 - search the forums for "OKD") I see:

• The Download throughput is low - 65-80 mbps, but not smooth
• The Upload is worse - about 20mbps.
• The Combined plot shows serious decrease in rates, likely because the packet loss and significant bufferbloat/latency increase interferes with the TCP connections.
• Latency for download is higher than expected, but still less than 100msec
• Latency for upload gets very high - averaging 250msec; peaking to 500msec.
• The Packet Loss chart shows occasional packet loss during the Download; a large burst of packet loss during the Upload, and continuing packet loss for the Combined test.
• What other observations are there from this plot?

WiFi from Dining Room

This looks a little better...

• Download is about 100mbps, but still spiky.
• Upload is a little higher, perhaps about 150mbps. However there is a pattern of regular latency drops, which are currently unexplained.
• The Combined throughput plot shows the sum (purple) about the same as the Upload throughput, with the Download (green) considerably lower than when downloading alone.
• Latency for all plots is lower than the previous chart, but still peaks over 150msec numerous times.

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FAQs

• How can I run the Crusader Server? You need to use another computer connected via Ethernet.
  • The examples above use a Raspberry Pi.
  • You could also run the Crusader Server on an Ethernet-connected computer, either building the software locally, or running it in a Docker Container. (This is becoming remarkably easy.)
  • On the router if it's fast enough. High-end routers, especially those that support Docker containers, probably have enough CPU power both to source and route packets at the full rate. (How could I tell if it's fast enough?)
• Why is that second test so terrible? What can I do about it?