Lossless Compression Brings Possible Speedups To Skylake Linux Mesa Driver

Written by Michael Larabel in Intel on 8 February 2016 at 02:24 PM EST. 1 Comment
Topi Pohjolainen of Intel posted a set of 23 patches today for providing compression of single-sampled color surfaces / lossless compression within the Intel Mesa driver for Skylake "Gen9" and newer.

The Intel OTC developer described this compression feature as:
This series enables compression for single sampled color surfaces, also referred to as "lossless compression". This is yet only for driver internal use easing pressure on memory bandwidth and caches when writing, blending and sampling surfaces uing gpu.

As a side effect the need for color buffer resolves after fast clears is also decreased. Current understanding is that sampling engine doesn't understand meta data (auxiliary buffer) for single sampled fast cleared surfaces. However, if the meta data is written with lossless compression enabled, even sampling engine is capable of reading both the color buffer and the auxiliary, and resolves can be omitted in those case.
The code is currently up for review via this patch series for the Intel Mesa driver.

Enabling this lossless compression for Gen9 graphics in the Mesa driver yielded performance improvements by 8~9% in GFXBench while the Unigine Heaven tech demo regresses by about 2%, likely due to overhead elsewhere from these code changes.
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