i965: Make brw_clear_cache NULL out stale program pointers

Graphics / Mesa 3D Graphics Library / Mesa - Kenneth Graunke [whitecape.org] - 12 February 2016 22:35 UTC

The L3 partitioning code tries to look at all programs - both render programs (VS/TCS/TES/GS/FS) and compute (CS).

After calling brw_clear_cache, all prog_data pointers are invalid and point to freed data. The intention was that flagging the dirty bits for all programs would cause the next draw call to re-run the atoms for each program stage, uploading new programs and installing new, valid pointers.

However, this doesn't quite work in our new multi-pipeline world. When drawing or dispatching a compute workload, we only consider the programs for the appropriate pipeline: drawing sets up VS/TCS/TES/GS/FS, but not CS, and vice versa. This leaves pointers dangling a bit longer than intended.

The L3 configuration code tries to inspect the prog_data for all shader stages, so that we avoid having to reconfigure it when swapping back and forth between render and compute workloads. So we can't have dangling pointers.

The fix is simple: have brw_clear_cache NULL out stale prog_data pointers, making it safe to inspect. The next L3 configuration pass will see either the render shaders or compute shader as missing for one go around, but will pick them up when both pipelines have run.

In other words, we'll simply reconfigure L3 twice, which is safe, if a tiny bit wasteful - but then again, we just threw every compiled shader we had on the floor and started recompiling the from scratch, which is massively more wasteful, so it's not much of a concern.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93790

c8b0020 i965: Make brw_clear_cache NULL out stale program pointers.
src/mesa/drivers/dri/i965/brw_state_cache.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)

Upstream: cgit.freedesktop.org

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