A method of profiling the performance of a graphics unit when rendering a scene according to a graphics pipeline, includes executing stages of the graphics pipeline using one or more units of rendering circuitry to perform at least one rendering task that defines a portion of the work required to render the scene, the at least one rendering task associated with a set flag; propagating an indication of the flag through stages of the graphics pipeline as the scene is rendered so that work done as part of the at least one rendering task is associated with the set flag; changing the value of a counter associated with a unit of rendering circuitry in response to an occurrence of an event while that unit performs an item of work associated with the set flag; and reading the value of the counter to thereby measure the occurrences of the event caused by completing the at least one rendering task.