[Mesa-dev] GL_INTEL_performance_query & null hw query

[Lionel Landwerlin]

Meant to Cc Mark too :)

On 03/12/2019 21:24, Lionel Landwerlin wrote:
> Hi all,
>
> Our Windows drivers ships with a particular query in 
> GL_INTEL_performance_query called Intel_Null_Hardware_Query.
> The query doesn't report any counter. The query isn't even listed if 
> you go through the list using glGetNextPerfQueryIdINTEL().
> It's only returned using glGetPerfQueryIdByNameINTEL().
> When active, this query turns the draw operations & compute dispatches 
> into noop at the command streamer level.
>
> Applications like GPA [1] have been using this query to detect 
> bottlenecks on the CPU side since there is no work going beyond the 
> front end of the rendering engine. So you still exercise the full 
> stack (in our case i965/iris + i915).
>
> To minimize the work of getting GPA fully supported on i965/iris we 
> could implement the same behavior.
> Last time I asked (probably on IRC), it was kind of a no-go because 
> that is somewhat abusing the meaning/goal of queries (at the time, 
> applications like frameretrace didn't deal very well with a query 
> having no counters).
> I'm not particularly kind on having this either but I would like to 
> know other people's feel.
>
> Alternatively we have another extension providing the same feature [2].
> I sent patches for i965 a bit over 18months ago, but because people 
> started to using a patch implementing the Windows driver behavior, 
> this didn't get much traction.
> This will a require a change on the GPA side but
>
> Which way should we go?
>
> -Lionel
>
> [1] : https://software.intel.com/en-us/gpa
> [2] : 
> https://www.khronos.org/registry/OpenGL/extensions/INTEL/INTEL_blackhole_render.txt
>
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