There's two main parts to the stall, which aren't well illustrated by the diagram (I'll get on updating it): 1. Waiting for the resource to exit the command st

There's two main parts to the stall, which aren't well illustrated by the diagram (I'll get on updating it): 1. Waiting for the resource to exit the command stream (wined3d_resource_wait_idle). 2. Waiting for the CS thread to finish after the map (occurs in wined3d_cs_map). It's a pipeline stall because the D3D thread has to wait for the CS thread to do things, and thus is unable to dispatch more commands to the CS (and thus the GPU) during this time. I don't consider the actual glMapBufferRange to be part of the stall. Edit: saw your edit :)