Out-of-Order Rasterization On RadeonSI Will Bring Better Performance In Some Games
Written by Michael Larabel in Radeon on 9 September 2017 at 08:30 AM EDT. 11 Comments
AMD developer Nicolai Hähnle has published a set of patches today for adding out-of-order rasterization support to the RadeonSI Gallium3D driver. Long story short, this can boost the Linux gaming performance of GCN 1.2+ graphics cards when enabled.

Nicolai posted this patch series introducing the out-of-order rasterization support. This is being used right now for Volcanic Islands (GCN 1.2) and Vega (GFX9) discrete graphics cards (though support might be added to other GCN hardware too). It can be disabled via the R600_DEBUG=nooutoforder switch.

This out-of-order rasterization support is also wired in for toggling it and some attributes via DRIRC for per-game Linux profiling in order to enable/disable depending upon where this helps Linux games or otherwise causes issues.

Nicolai has posted an explanation of out-of-order rasterization on his blog for those interested in a technical explanation, " Out-of-order rasterization can give a very minor boost on multi-shader engine VI+ GPUs (meaning dGPUs, basically) in many games by default. In most games, you should be able to set radeonsi_assume_no_z_fights=true and radeonsi_commutative_blend_add=true to get an additional very minor boost. Those options aren't enabled by default because they can lead to incorrect results."

Once the patches land in Mesa Git (or while still in patch form, if I magically find extra time before then), I intend to try out the support to see their impact on popular Linux games.
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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