adaptive sync

README.md

@@ -75,8 +75,51 @@ echo 3 | sudo tee /sys/class/drm/card*/device/pp_dpm_mclk
   with `adaptive_sync off` games run without it.
 - To turn off FreeSync for a single game (Xorg): `adaptive_sync=false %command%`
   (Steam launch options).
+- Login greeters (SDDM, LightDM, ...) are fullscreen and mostly static, so VRR
+  drops to the bottom of the range and flickers. `mesa/drirc` disables it for
+  any `*greeter*` executable; install system-wide (greeters don't read `~/.drirc`):
+```bash
+sudo cp xorg/20-amdgpu.conf /etc/X11/xorg.conf.d/
+sudo cp mesa/drirc /etc/drirc
+```
 ![stones](./screenshots/Screenshot_20240503_095414.png)
 
+## Shader cache (Steam)
+
+With Steam's *Shader Pre-caching* off (it re-downloads caches for every game
+almost daily), Steam points Mesa at a temporary
+`~/.local/share/Steam/shader_cache_temp_dir_*` and deletes it when the game
+exits, so every session recompiles shaders (hitches everywhere, every time).
+Steam only sets the legacy `MESA_GLSL_CACHE_DIR`, so the newer variable wins.
+Set it session-wide (i3 is started by SDDM, `environment.d` doesn't reach
+Steam). The cache lives in `/var/cache` so `~/.cache` cleaners don't wipe it,
+with one private subdir per user: Mesa creates its dirs `0700`, so a single
+shared dir can't work (and would let users poison each other's shaders).
+`/etc/environment` can't expand `$USER`, so use `/etc/profile.d` (SDDM's
+X11/Wayland sessions and TTY logins source it). Run as your normal user, not
+from a root shell (`~` and `$USER` must be yours), with Steam closed:
+```bash
+sudo mkdir -p /var/cache/mesa_shader_cache
+sudo chmod 1777 /var/cache/mesa_shader_cache   # like /tmp: anyone creates own subdir
+mv ~/.cache/mesa_shader_cache /var/cache/mesa_shader_cache/$USER  # no sudo: keeps ownership
+sudo sed -i '/^MESA_SHADER_CACHE_/d' /etc/environment
+sudo tee /etc/profile.d/mesa-shader-cache.sh >/dev/null <<'EOF'
+export MESA_SHADER_CACHE_DIR="/var/cache/mesa_shader_cache/$USER"
+export MESA_SHADER_CACHE_MAX_SIZE=10G
+export PRESSURE_VESSEL_FILESYSTEMS_RW=/var/cache/mesa_shader_cache
+EOF
+```
+The last line matters: Steam runs games (native and Proton) in the Steam
+Linux Runtime container, which shares `$HOME` but gives the game its own empty
+`/var`. Without it the cache is written to a tmpfs inside the container and
+thrown away when the game exits.
+Re-login, then check it's yours and persists after playing (should print > 0):
+```bash
+echo $MESA_SHADER_CACHE_DIR; ls -ld $MESA_SHADER_CACHE_DIR   # owner must be you
+find $MESA_SHADER_CACHE_DIR -mmin -60 -type f | wc -l
+```
+Deleting the cache is harmless: shaders just recompile (stutter) on first use.
+
 ## Installing dependencies
 
 Package availability differs between distros — Arch has everything below in the
@@ -191,9 +234,9 @@ sudo emerge --ask games-util/gamemode
 
 Adaptive sync (sway): the desktop runs at a fixed 240 Hz with VRR off, because
 sway only renders on change and idle frame rates fall below the panel's 48 Hz
-floor (out of LFC range → flicker). `sway/scripts/vrr-follow` turns VRR on for
-DP-1 only while the visible workspace has a fullscreen window; `lock-now` turns
-it off while locked. Needs `jq`.
+floor (out of LFC range → flicker). gamemode turns VRR on for DP-1 while a
+game runs and off when it exits (install `gamemode/gamemode.ini` to
+`~/.config/gamemode.ini`); `lock-now` turns it off while locked.
 
 ### GPU monitoring & tuning