The Autotuner in Mesa's Turnip drivers dynamically selects between GMEM (tile-based, on-chip memory) and sysmem (direct system memory rendering) modes to optimize performance for Adreno GPUs. It uses heuristics to make decisions but can be overridden with TU_DEBUG options for debugging or to address specific issues. While effective in many cases, the Autotuner may struggle with certain workloads or newer GPUs, requiring manual configuration or updated driver variants for optimal performance. Which is why the unsupported GPUs mentioned above may need GMEM.