15.1-RELEASE increased input latency on amdgpu

J

jb82

Hey,

I also tried what's mentioned in this Reddit post [1] (see below): typometer, Xorg/dwm, picom or no picom, external display. I used the old 15.0-RELEASE boot environment to compare the two with similar findings:

15.1-RELEASE typometer reported latency substantially increased compared to the same user-space stack on 15.0-RELEASE. The increase is there both with and without compositor running. Approx +40-80 %.

I've learned that some scheduler related changes were applied in 15.1-RELEASE, but no idea yet whether those might be related. Does anybody have any ideas? It's interesting, at least.

Scheduler issues?

[1] https://www.reddit.com/r/freebsd/comments/1uklfl6/a_bit_higher_input_latency_on_151release_compared/
 
cracauer@ said:
How exactly is typometer measuring what thing?
Click to expand...
Not expert on that thing but my assumption goes like this: You point it at some X11 window, it draws a couple of points and finds details about how they're drawn. Then it starts firing key events leading to dot drawing while simultaneously waiting for them to be rendered on the X11 screen. Naively, I'd say it just looks for the pixels it expects. On a laptop, with the native screen, xterm, st and similar easily achieve <3 ms avg latency without compositor. On external displays it's definitely more tricky, but 15.0 was showing substantially better numbers. I'm just interested in why so, assuming that on the X11 (user-space) side nothing has substantially changed between those two releases.
 
Well, the scheduler is unlikely to be responsible anyway if you have no competing workloads running and the graphical interface is the only thing that wants to be scheduled.

Big question is whether FreeBSD or the display server are responsible. You could try booting the 15.0 install with a 15.1 kernel.
 
Oh an aside, what is the value that latency becomes "visible" to the user?
80% or round up to double on 10ms means 20ms at the extreme. I'm not sure I can detect the difference between me hitting a key and the character displays in the window of 10 ms or 20ms.
But yeah, I'm old and don't play games so maybe it doesn't matter to ME but to someone playing games? It may matter. If you are playing online games with udp traffic, drop 2 packets and the latency is irrelevant.
 
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