[Mesa-dev] shader cache backward compatibility

Bas Nieuwenhuizen bas at basnieuwenhuizen.nl
Fri Aug 31 09:40:16 UTC 2018


On Fri, Aug 31, 2018 at 11:32 AM Alexander Larsson <alexl at redhat.com> wrote:
> Hi, I'm the developer behind flatpak (https://flatpak.org/) and we've
> recently run into some issues with the mesa shader cache. Flatpak has
> a app/runtime split where the runtime is shared between app and
> provides /usr. The runtime contains a version of mesa, but this can be
> overridden by runtime extensions to add other OpenGL drivers.
> Each app has a separate $XDG_CACHE_HOME, pointing into the per-app
> writable storage. For example, gedit has
> XDG_CACHE_HOME="/home/alex/.var/app/org.gnome.gedit/cache". This
> causes mesa to store the shader cache per-app in
> $XDG_CACHE_HOME/mesa_shader_cache.
> In the regular case this works fine, but sometimes the version of mesa
> is changed, with the shader cache being left in place. For example,
> sometimes we update the mesa version in the runtime, and sometimes the
> app switches to a new runtime which has a different mesa version.
> Such updates have caused a lot of issues for us, ranging from direct
> crashes at startup as in
> https://github.com/flatpak/flatpak/issues/2052 and sometimes just
> super-slow performance. In all cases, blowing away the shader cache
> directory fixed all issues.
> The steam flatpak has a bunch of workaround for the cache:
>   https://github.com/flathub/com.valvesoftware.Steam/blob/master/steam_wrapper/steam_wrapper.py#L35
> But we can't expect every app to do this.
> So, my question is, is the cache supposed to be backward compatible,
> or at least versioned? Are we missing something in our mesa builds to
> make that work? Is this fixed somewhere with a patch i can backport?
> And if not, do we need to add some magic to flatpak to automatically
> clean up the shader cache after an update?

It is supposed to be versioned automatically by mesa.

> --
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
>  Alexander Larsson                                Red Hat, Inc
>        alexl at redhat.com         alexander.larsson at gmail.com
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