Bug 111267

Created attachment 144918 [details]
Zip file containing RenderDoc captures, a vktrace and two screenshots

During development of a Vulkan application in Rust, we have identified what appears to be a graphics driver bug. The minimal example that reproduces this is a simple application that does the following each frame:

- Start a compute pass
- Set the compute pipeline
- Dispatch the compute pass, which can even be an empty shader
- Start a render pass
- Set the render pipeline
- Draw a simple geometry with many instances (200k)
- Draw a simple geometry with two instances

The observed behavior is flickering of the two instances that are rendered last between frames.

A workaround is to set the pipeline again after the first draw call. This will remove the flickering.

I have attached two captures from RenderDoc of a good and a bad frame, where the bad frame is missing the geometry (which causes the flickering). However, upon loading both frames in RenderDoc again, the geometry is always shown - indicating a possible driver bug.

I have also attached a vktrace, which on an affected machine reproduces the flickering during a vkreplay. The flickering will also vary between replays.

Finally, I have attached two screenshots that illustrate the difference between good and bad frames.

Source code to reproduce the issue can be found in the following branch of gfx-rs/wgpu-rs:

https://github.com/dragly/wgpu-rs/tree/dragly/comp-issue

It can be tested by running

> cargo run --features vulkan --example cube

System information:

Machine: Dell XPS 15 9570
Chipset: CM246
OS/Distro: KDE Neon 5.16.4 (based on Ubuntu 18.04)

Output of version information commands:

> inxi -G -c0
Graphics:  Card-1: Intel Device 3e9b
           Card-2: NVIDIA GP107M [GeForce GTX 1050 Ti Mobile]
           Display Server: x11 (X.Org 1.19.6 ) drivers: modesetting (unloaded: fbdev,vesa)
           Resolution: 3840x2160@60.00hz, 2560x1440@59.95hz
           OpenGL: renderer: Mesa DRI Intel UHD Graphics 630 (Coffeelake 3x8 GT2)
           version: 4.5 Mesa 19.2.0-devel (git-3a22a8b 2019-07-31 bionic-oibaf-ppa)

> pkg-config --modversion libdrm
2.4.99

> uname -r
4.15.0-55-generic

Note: I am currently running a more recent set of drivers to see if an update would help, but the issue is also there for the default drivers that come with Ubuntu 18.04.