[Bug 79029] New: INTEL_DEBUG=shader_time is full of lies

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=79029

          Priority: medium
            Bug ID: 79029
          Assignee: idr at freedesktop.org
           Summary: INTEL_DEBUG=shader_time is full of lies
        QA Contact: intel-3d-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: All
          Reporter: kenneth at whitecape.org
          Hardware: Other
            Status: NEW
           Version: git
         Component: Drivers/DRI/i965
           Product: Mesa

INTEL_DEBUG=shader_time reports that almost 0 time is spent in the vertex
shader in a microbenchmark (OglTerrainFlyInst).  However, the FS is really
simple, and the VS is pretty large.  I managed to cut roughly 50% of the VS
instructions, and that roughly doubled the performance.  So clearly the VS is
important.

Using performance monitoring, it looks like the VS actually takes up ~70% of
the time.  So, shader_time is just full of lies.  It appears that it's
undercounting the VS time in Unigine Valley as well.

I believe the timestamp register is getting reset in almost every VS, so we
just count 0 most of the time.

Perhaps it can be improved?  Perhaps we need to develop something better?

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