Linux DRM Dumb Buffers are slow to read, not write

Small experiments in the use of libliftoff to try out the modern Linux graphics stack drove home quite how slow DRM “dumb buffers” can be, but also that it’s reading that’s slow, not writing . Reading from a “dumb buffer” on my AMD GPU is orders of magnitude slower than reading from RAM. It can take seconds to read out a full 4k frame. It’s roughly a thousand times slower than reading RAM. 1 2…