[Bug 80792] [IVB/HSW/BYT-M Bisected]3D ( SynMark2_v5.3.0 /SynMark2_v6.0 /Lightsmarkv2008 &/warsow_v1.0 /GLBenchmarkv2.7.0/GpuTest GiMark) performance reduced 20%~90%

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=80792

--- Comment #10 from Eero Tamminen <eero.t.tamminen at intel.com> ---
I tested clean master.


Btw. the patch comment states:
------------
 So far we have been using CL_INVOCATION_COUNT to resolve this query
 but this is no good with streams, as only stream 0 reaches the
 clipping stage. Instead we will use SO_PRIM_STORAGE_NEEDED which
 can keep track of the primitives sent to each individual stream.

 Since SO_PRIM_STORAGE_NEEDED is related to the SOL stage and according
 to ARB_transform_feedback3 we need to be able to query primitives
 generated in each stream whether transform feedback is active or not
 what we do is to enable the SOL unit even if transform feedback is not
 active but disable all output buffers in that case. This effectively
 disables transform feedback but permits activation of statistics
 enabling SO_PRIM_STORAGE_NEEDED even when transform feedback is not
 active.
----------

But looking at the spec:
----------
When geometry shaders are not used, or when an old geometry shader not
writing multiple streams is used, all vertices produced by the GL are
directed at the stream numbered zero.  The set of transform feedback-
related query targets is extended to accommodate multiple vertex
streams, so it is possible to count the number of processed and
recorded primitives for each stream separately.
----------

-> As the issue was with statistics for non-zero streams and those are only
used with geometry shaders, it seems that clipper invocation count can
still be used if there's no geometry shader.  None of the programs which
had regressed hugely, used geometry shaders.

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