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darling-lol/docs
3AvisD efc92dfb04 fix(launcher): keep Mesa's shader cache on the host
Mesa derives its shader disk cache from $HOME. Inside the guest that is
/Users/<user>, which does not exist on the host filesystem, so Mesa could not
create the cache and disabled it, once per process:

    Failed to create /Users/<user> for shader cache (Permission denied)---disabling

One launcher log contained 212 of those lines, and no shader compiled by one
process was reused by another process or by the next start: the client and the
game recompiled every shader on every launch, spending CPU at startup for no
gain.

Mesa is host code loaded into the guest and reads MESA_SHADER_CACHE_DIR verbatim,
so point it at a host directory; Mesa creates mesa_shader_cache/ (client and game
shaders) and radv_builtin_shaders/ below it. A non-empty value from the caller is
preserved, and a directory that cannot be created leaves the previous behaviour
instead of ending the launch.

Observed on a Radeon RX 550 with radv: no shader-cache failure after the change,
and 434 files / 5.6 MB written during one client start, still growing while the
client ran. The cache is reused from the second start on, which lowers the
client's CPU use while it starts; the startup-time gain itself has not been
measured separately.
2026-10-18 12:18:33 -06:00
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