tmux 2.4 consumes a lot of CPU

[maotora]

Hello,

Recently after I updated my system I was upgraded to tmux -V 2.4 which was kinda cool except when it started consuming a lot of CPU.

I'm not sure what (in tmux) is causing this asked yesterday in the IRC but most said there systems were okay (even ones using same linux distro).

I'm using ArchLinux, and here is some screenshot to explain a bit more.

Before tmux started

After tmux started with 2 sessions opened and 5 panes (combined).

htop after tmux started.

Now, I have to say 2.3% CPU is huge for tmux with 5 panes, but this can go up to 50% when I keep my tmux running. I'm also including sensors results cause that's what terrifies me more than the CPU usage.

My tmux configurations I should also add that I tried commenting out tmux powerline and tmux plugins but this did not help.

My hardware info if it's important.

[nicm]

tmux.conf?

[maotora]

@nicm I just posted it it's a bit long so I thought I should use a link instead.

[nicm]

Can you reproduce without a tmux.conf?

[maotora]

Oddly enough, it started and stayed smooth.
But what's in my tmux.conf that makes it aggressive then?

Update.

It's powerline not sure why, but only the tmux one does this in tmux though (as I'm using powerline in zsh too).
I tried commenting out the line sourcing powerline and it did the trick.

Thank you for your support @nicm

[nicm]

I don't know, start commenting stuff out until you find the problem? I'd start with all the tpm stuff at the end.

[pjcj]

I'm not convinced this is a powerline problem. See my analysis in the bug referenced above.

Is it possible that display -p is triggering a status line redraw?

[nicm]

I don't know if it is powerline or not but I'm not going to try and work it out from a 200 line config file.

I don't think display -p does a redraw and it doesn't seem to for me. What do the tmux logs look like when you do it? Do you see it sending the status line to the terminal (look for "[display-message]" then lines starting "/dev/ptywhatever:" and your status line contents).

[nicm]

I think 7d23d01 is possibly going to be hurting you here. But this would be a lot quicker if you could please create a small standalone config file to reproduce then show me it and tmux logs demonstrating the problem.

[nicm]

Hmm no you are using status-right so maybe something else.

[jungle-boogie]

FYI, here's another issue related to powerline, tmux and high CPU usage: #361

[pjcj]

I have narrowed down the problem:

.tmux.conf has a single line: set-option -g status-right "#(echo #D)"

Run tmux new in two terminals.

Workaround: set-option -g status-right "#(echo '#'D)"

I trust this will be sufficient to show the problem. Thanks!

[nicm]

Great, I can reproduce with this.

So the problem is because tmux will bypass the "only once a second" rule for jobs (that is, #()) where the expanded form has changed. And because you have two clients with different sessions, it is always changing because the two clients have different active panes so for one #D will be %0 and for the other it'll be %1.

The idea behind this was that people who have, for example, #(myscript #D) in windows with multiple panes don't have to wait for a second before the status line updates when they switch pane.

I think the best way to fix this for both cases is by tying the job to a particular client when possible (so each client has its own list of jobs). Please try this: a.diff.txt

[nicm]

Your workaround works because the expansion is happening at a different point. The expanded command is "echo '#'D" which never changes, so tmux runs it at most once a second. The expansion of #D happens on the output of the echo, instead of on the echo command itself:

#(echo #D) -> #(echo %0) -> %0 -> %0
#(echo '#'D) -> #(echo '#'D) -> #D -> %0

[pjcj]

That fix looks to be working fine. Thanks for identifying and fixing it so quickly!

[m1cr0man]

Hello!

A couple of days ago I ran into this issue myself and reported it on the IRC as I didn't have time to make an issue and help debug it. I just tried that patch myself and it seems to have corrected the issue for me too. I'm not using Powerline but I do have my own quite complicated status-left and -right texts.

Thanks for resolving this one so quickly! It was a bummer having my status bar disabled for the last few days 👍

[nicm]

Applied now, thanks.

[lock]

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