Debug Performance Regressions on 0.20 Vulkan

[guusw]

Hey, I recently tried upgrading from 0.19.1 to 0.20 and noticed I get half the performance using vulkan as I did previously.

I did some profiling and noticed all application code is the same except for one vkQueueSubmit taking up 11ms
I suspect something is waiting for an operation to complete which did not happen previously.

It's worth nothing that I perform a readback from a texture, although it happens asynchronously using wgpuBufferMapAsync.

Below I have provided two renderdoc captures (before/after the upgrade)
The rendered items are identical, the only difference I could notice is some fences at the start of the 0.19 capture

Let me know if I can provide any other information to help.

renderdoc.7z.zip

[AdrianEddy]

FWIW, I noticed 2x Vulkan performance decrease but not related to wgpu, but after updating the NVIDIA driver from 535 to 550. Is your GPU driver the same?

[guusw]

516.94, will try with the most recent one.

[Wumpf]

Might also be worth trying against the changes on #5681
We've been meaning to put this in a patch release because there's all sort of problems prior to that PR

[vntec]

I've had similar performance problems with Vulkan and v0.20.0.

After upgrading, I noticed mouse input being very unresponsive in my engine. The NVIDIA overlay reported a render latency of ~120ms at 144FPS (Fifo). The frametimes were similar to v0.19.4 (latency was ~11ms). A similarly high latency occurred at higher framerates with VSync off (Immediate).
Initially, I suspected my own engine code, but the same problem occurred when I tested the official wgpu examples. The ash examples did not display this behavior.
I'm not entirely sure how NVIDIA exactly measures "render latency", although it seems to be something like "time from render queue to actual presentation".

Upgrading my driver to 555.85 did not help.

I suspect this has something to do with the recent synchronization changes in #5681.

[Wumpf]

I suspect this has something to do with the recent synchronization changes in #5681.

any chance you could check against latest trunk? We want to release a patch with that PR soon

[LukasKalbertodt]

I also ran into this problem after updating to v0.20. It doesn't seem like the framerate has decreased, but the latency increased a lot in Fifo mode. I also use wgpuBufferMapAsync but never block on it.

I use an Nvidia RTX 470 with driver version 550.78, on Linux, winit 0.30, whole desktop running at 60fps.

I did update to the latest trunk as suggested, but unfortunately that did not fix the issue.

Noticing latency manually is a bit error prone so I did the following: just print to the terminal whenever an button press is detected. The button press leads to camera motion and thus to a notable change in the rendered image. I then screen captured terminal + wgpu window and finally counted the frames between "terminal prints event" and "effect visible in rendered image". I know this is far from a perfect measurement of latency, but the trend is clear: before the wgpu 0.20 update, there were 2 frames delay, with wgpu 0.20 it's 6 frames, with c745863 it's also 6.

In Immediate present mode, there doesn't seem to be a problem, I think.

[vntec]

I suspect this has something to do with the recent synchronization changes in #5681.

any chance you could check against latest trunk? We want to release a patch with that PR soon

I just checked against the latest trunk and it does seem a bit better. With VSync, the latency is reduced from ~120ms to ~30ms and it's noticeably more responsive. However it's still not as good as v0.19.4 (11-15 ms).
I think the problem still applies to Immediate present mode, but the impact is generally less noticeable since the frametimes and latencies are lower (for simple scenes).

[jimblandy]

We would definitely like to address this, but so far in this issue it's hard to discern how we can actually debug this. A reduced test case that we can run locally to see the problem ourselves would make progress a lot easier.

[hecrj]

Just chiming in to say that I have noticed this regression when working on the upgrade in iced, even after #5681—and it is one of the main reasons the upgrade has not been merged yet (iced-rs/iced#2417).

However, it seems I can only reproduce the regression in debug mode. release builds seem to both have similar performance. Talking about render time, specifically. Not latency.