ARB_shader_clock Lands For Intel's Mesa Driver

[phoronix]

Phoronix: ARB_shader_clock Lands For Intel's Mesa Driver

Over a few commits yesterday, the Intel Mesa driver now exposes ARB_shader_clock support...

http://www.phoronix.com/scan.php?pag...er_clock-Intel

[Remdul]

Yeah, I found the usage conditions to be a bit...constraining. I guess it is mainly intended for comparing the timing results of the same shader (and seemingly, same input data) against the same shader but slightly different code. I.e. it can be used to find the best shader code path (permutation) for a given shader compiler/GPU. My guess is that early-z, caching and other temporal coherency hacks make it very difficult to otherwise time the shader execution (for a given vertex/fragment). I think that's why they included the 'not constant' & 'undefined units' comment. Or you'd be more like timing the drawcall (although per vertex/fragment; with all optimizations involved) and not the shader execution itself.