RADV Vulkan Driver Adds Option To Force Smart Access Memory Behavior

The latest "Smart Access Memory" work by the open-source AMD Radeon graphics driver stack is an option for the RADV Vulkan driver to force the "SAM" behavior even if the system is not advertising all the video RAM as visible or even if using APU graphics.

With the RADV Vulkan driver optimizations around Smart Memory Access / Resizable BAR, it has been contingent on all of the vRAM being visible, having discrete/dedicated video memory, and not using the "nosam" override to disable the behavior. But new to Mesa 21.1 is a "sam" option to override into forcing the driver to enable its Smart Access Memory behavior even if the system is not advertising the support or even if not having dedicated video memory.

RADV co-founder Bas Nieuwenhuizen added the option on the basis of "So that people without large BAR can try this out."

With Mesa 21.1, which should be released in late May or early June, can force enable this driver SAM behavior with the RADV_PERFTEST=sam environment variable prior to launching Vulkan games/applications. If all goes well, the optimizations will be flipped on to allow moving more driver internal objects to video memory.