A small line of code ended up costing Intel GPUs a 100x reduction in RT performance


No, I didn’t get the number wrong in the title!

Intel Linux Graphics Processor driver developers recently released an update for the GPU Arc providing a boost up 100x in ray tracing performance. To think about it, where is that 100x loss in performance come first then. A difference of 100x is not something to be taken lightly, I mean wouldn’t you notice if you had $1 instead of $100.

Phoronix indicates that a patch has been introduced in the open-source Intel Mesa Vulkan driver by Intel Linux faithful engineering graphics driver Lionel Landwerlin. The developer’s comments are rather interesting as he literally said “Like a 100x improvement (no kidding)”.

Intel Apparent Failure in Drivers | Coming

So what was wrong? Well, it’s not rocket science, and that’s a good thing. Originally, the vulcan pilot ensured that any memory required for Vulcan RT would be stored locally (on the very quickly on-board memory). Even if you are not a developer of any kind, you should know that faster equals better, keep that in mind as it will come in handy.

Basically, everything was perfect except for one line. They forgot to include the line that actually allocates memory, rendering all their efforts null and void. What happened next? Well the vulcan pilot use it Slow down on-board memory causing massive performance hits.

After setting a flag for “ANV_BO_ALLOC_LOCAL_MEM”, the Vulkan driver started using the Faster on-board memory leading to the above 100x gain in performance. Mesa 22.2 containing the above mentioned code along with other improvements should reach end users by the last week of August.

This shows the importance of good drivers, as a single line of code can lead to a massive increase of more than 100x in performance. Intel had its fair share of struggle with driver optimization. Intel’s real competitor was the RTX-3070 and leaked references show it to be somewhere in the territory of the RTX-3070 although gaming performance varies.

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