High CPU load when network traffic page left open

[willcl-ark]

Is there an existing issue for this?

• I have searched the existing issues

Current behaviour

Possibly related to #466

Running Bitcoin Core version v25.99.0-04265ba9378e

When running bitcoin-qt with an additional network traffic window open, after some time CPU usage on a single core starts to thrash between 60-100%. The CPU thrashing will (immediately) drop when the network traffic window is closed.

Expected behaviour

Viewing the network traffic page should not use 100% CPU or cause thrashing.

Steps to reproduce

steps

• Run bitcoin-qt, open network traffic and wait some time? I think the graph needs to include a wide range of datapoints for this (rendering?) bug to occur (see below screenshots).

actions

I ran perf for 30 seconds on bitcoin-qt while CPU was thrashing, but it seemed to only show a lot of time spent in libQT5Gui.so, which doesn't seem particularly helpful.

I noticed that the CPU spikes seem to only be present when the graph is well-populated with many variously-valued data points, like this:

However CPU usage drops if there is a large spike in network activity, which causes a low level of datapoint variation (plus one large spike), like this:

Relevant log output

Nothing of interest was present in the logs.

How did you obtain Bitcoin Core

Compiled from source

What version of Bitcoin Core are you using?

v25.99.0-04265ba9378e

Operating system and version

Ubuntu 23.04

Machine specifications

OS: Ubuntu 23.04 x86_64
CPU: 11th Gen Intel i7-11700K (16) @ 3.800GHz
GPU: NVIDIA GeForce RTX 3060 Ti
Memory: 64162MiB
HDD: Samsung SSD 990 PRO 2TB
MB: Z590 AORUS ELITE AX
Kernel: 6.2.0-33-generic
Resolution: 3840x2160
WM: i3
Terminal: tmux
Shell: fish 3.6.1

[willcl-ark]

This graph "shape" also exhibited the same behaviour, so it seems reproducible (for me).

[fanquake]

Is this only an issue with master (regression) or also a problem if you run 25.0 or 25.1rc1?

[willcl-ark]

This also appears to occur for me on v25.0, So not a regression on master. e.g. with the following graph:

I see CPU thrashing of 50 - 90%, and get this similar-looking perf report: https://tmp.256k1.dev/23_10_bitcoin_qt_25.0_cpu.svg

[maflcko]

Which version of qt? Does it also happen with a previous release (statically compiled)?

[willcl-ark]

Sorry for the slow reply, these were both compiled with libqt5gui5 version 5.15.8+dfsg-3.

Which previous release would you like me to try?

[maflcko]

any previous release, or the 26.0rc1 (I am only wondering about guix compilation vs local compilation)

[willcl-ark]

Tested again with 26.0rc2 binary from bitcoincore.org, and the issue is still present for me. So long as the graph content is relatively "varied", then one CPU constantly thrashes between ~60-100%.

Seems to happen even more readily if I set the scale to 5m where even with fewer data points shown (I think) it pretty much just pins a single core to 100%

I guess it's possible that this is something specific to my setup, and not a Bitcoin Core/QT issue; if so then I'm not too worried as I don't use the QT program that often (and don't need to leave the network traffic page open in any case).

Let me know if there's anything else useful I can do to help debug. I think first it might be good to have a reproduction from someone else...