zink (on RADV) limits "vblank_mode=0 glxgears" to ~180 fps

System information

System:
  Host: thor Kernel: 5.13.7+ x86_64 bits: 64 compiler: gcc v: 10.2.1 
  Desktop: GNOME 40.2 tk: GTK 3.24.29 wm: gnome-shell dm: GDM3 
  Distro: Debian GNU/Linux 11 (bullseye) 
CPU:
  Info: Quad Core model: AMD Ryzen 7 3700U with Radeon Vega Mobile Gfx 
  bits: 64 type: MT MCP arch: Zen rev: 1 cache: L2: 2 MiB 
  flags: avx avx2 lm nx pae sse sse2 sse3 sse4_1 sse4_2 sse4a ssse3 svm 
  bogomips: 36727 
  Speed: 2182 MHz min/max: 1400/2300 MHz boost: enabled Core speeds (MHz): 
  1: 2182 2: 3699 3: 1481 4: 1624 5: 1682 6: 1473 7: 2522 8: 2404 
Graphics:
  Device-1: AMD Picasso vendor: Lenovo ThinkPad E595 driver: amdgpu 
  v: kernel bus-ID: 05:00.0 chip-ID: 1002:15d8 
  Display: wayland server: X.Org 1.21.0.99 compositor: gnome-shell driver: 
  loaded: modesetting alternate: ati,fbdev,vesa resolution: 1920x1200~60Hz 
  s-dpi: 96 
  OpenGL: renderer: AMD Radeon Vega 10 Graphics (RAVEN DRM 3.42.0 5.13.7+ 
  LLVM 12.0.0) 
  v: 4.6 Mesa 21.3.0-devel (git-fd62e0b799) direct render: Yes 

Describe the issue

vblank_mode=0 glxgears is limited to ~180 fps (~3x the refresh rate?):

GL_RENDERER   = zink (AMD RADV RAVEN)
GL_VERSION    = 3.0 Mesa 21.3.0-devel (git-6bfbce0447)
[...]
819 frames in 5.0 seconds = 163.561 FPS
893 frames in 5.0 seconds = 178.518 FPS
895 frames in 5.0 seconds = 178.861 FPS

Regression

Yes, bisected to !12090 (6bfbce04).

With the previous commit:

GL_RENDERER   = zink (AMD RADV RAVEN)
GL_VERSION    = 3.0 Mesa 21.3.0-devel (git-de2da3dadf)
[...]
6287 frames in 5.0 seconds = 1257.265 FPS
6398 frames in 5.0 seconds = 1279.521 FPS