[Bug 104335] [OpenGL CTS][SKL,KBL] KHR-GL45.vertex_attrib_64bit.limits_test occasionally fails

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=104335

            Bug ID: 104335
           Summary: [OpenGL CTS][SKL,KBL]
                    KHR-GL45.vertex_attrib_64bit.limits_test occasionally
                    fails
           Product: Mesa
           Version: git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/DRI/i965
          Assignee: intel-3d-bugs at lists.freedesktop.org
          Reporter: itoral at igalia.com
        QA Contact: intel-3d-bugs at lists.freedesktop.org

In my tests I have found this to have a low fail between 1% and 2%. If the test
is executed in a loop, then chances of it failing can be significantly
increased if we scroll the terminal fast for periods of 10+ seconds.

The problem seems somehow related to gl_InstanceID since every time I got this
to fail, the failure happens in subtests that use gl_InstanceID in the shaders
(with and without actual instancing draw calls being used).

Interestingly, replacing gl_InstanceID with 0 in the shader code seems to make
the problem go away entirely, which is quite surprising seeing that this test
has otherwise a very high pass rate and does actual instanced draw calls that
woudl rely on gl_InstanceID taking appropriate values.

FWIW, we have tested these in 4 different machines (SKL and KBL), and found
that on two of these which had 4.9 kernels we were unable to reproduce the
problem, where the other two where the problem existed the kernel was 4.10.

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