[STUMP] 0.9.9 Performance Regression

In my excitement about the module architecture, I updated from stumpwm
0.9.8 to the tagged 0.9.9, and have encountered a performance
regression:

Frequently, my UI hangs, including mouse movement and text entry into
emacs (the keyboard events don't get queued up, they are simply lost),
and if I have a process monitor open before this occurs, I can briefly
see my Xorg.bin server pinning a CPU in kernel-space, after I start
getting UI output again.

In terms of things I am doing atypically, I do have 61 windows open (I
had around 120 back in version 0.9.8 with no issues) with 8 actively
displayed at any given time, across four screens.

What steps do you lot suggest taking to more accurately isolate this
regression?

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