Coding Mistake Made Intel GPUs 100X Slower in Ray Tracing

Intel Linux GPU driver developers have released an update that results in a massive 100X boost in ray tracing performance. This is something to be celebrated, of course. However, on the flip side, the driver was 100X slower than it should have been because of a memory allocation oversight. Tom's Hardware reports: Linux-centric news site Phoronix reports that a fix merged into the open-source Intel Mesa Vulkan driver was implemented by Intel Linux graphics driver engineering stalwart Lionel Landwerlin on Thursday. The developer wryly commented that the merge request, which already landed in Mesa 22.2, would deliver "Like a 100x (not joking) improvement." Intel has been working on Vulkan raytracing support since late 2020, but this fix is better late than never. Usually, the Vulkan driver would ensure temporary memory used for Vulkan raytracing work would be in local memory, i.e., the very fast graphics memory onboard the discrete GPU. A line of code was missing, so this memory allocation housekeeping task wasn't set. Thus, the Vulkan driver would shift ray tracing data to slower offboard system memory and back. Think of the continued convoluted transfers to this slower memory taking place, slowing down the raytracing performance significantly. It turns out, as per our headline, that setting a flag for "ANV_BO_ALLOC_LOCAL_MEM" ensured that the VRAM would be used instead, and a 100X performance boost was the result. "Mesa 22.2, which includes the new code, is due to be branched in the coming days and will be included in a bundle of other driver refinements, which should reach end-users by the end of August," adds the report.

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