[Bug 100622] Depth-stencil clears trigger occlusion query object stalls

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=100622

            Bug ID: 100622
           Summary: Depth-stencil clears trigger occlusion query object
                    stalls
           Product: Mesa
           Version: 17.0
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/DRI/i965
          Assignee: intel-3d-bugs at lists.freedesktop.org
          Reporter: rsalminen at iki.fi
        QA Contact: intel-3d-bugs at lists.freedesktop.org

Created attachment 130759
  --> https://bugs.freedesktop.org/attachment.cgi?id=130759&action=edit
Test case which clears a depth-stencil attachment

Attached: test application to reproduce bug (see
https://github.com/rikusalminen/querystall for build scripts, etc. needs c99
compiler and CFLAGS).

Clearing a depth-stencil buffer when occlusion query (GL_SAMPLES_PASSED) is
enabled causes the following GL debug message (via glDebugMessageCallback):
GL_DEBUG_SOURCE_API GL_DEBUG_TYPE_PERFORMANCE GL_DEBUG_SEVERITY_MEDIUM  id: 0xb
CPU mapping a busy query object BO stalled and took 2.003 ms.

Clearing GL_DEPTH_COMPONENT24 target (instead of GL_DEPTH24_STENCIL8) does not
cause this behavior.

GL_TIME_ELAPSED or GL_PRIMITIVES_GENERATED queries do not give this error.

Here are some helpful notes from #intel-gfx IRC log:

21:12 < Kayden> ugh.  the query code is fine.
21:13 < Kayden> you're hitting lunacy in meta
21:13 < Kayden>
https://cgit.freedesktop.org/mesa/mesa/commit/?h=bb77745681e179b53ea64da7bc1987b57643b7b0
21:14 < Kayden> the clear isn't hitting our best-case scenario, and is falling
back to a meta use-GL-to-implement-GL path, that wants to disable occlusion
queries so our internal usage doesn't contribute fragments
21:14 < Kayden> and the way it does that stalls
21:14 < Kayden> we've been killing off this awful code for a while now, but
some bits are still left
21:21 < Kayden> wow, that's in a sorrier state than I thought :/
21:21 < Kayden> jekstrand: it looks like we always fall through to meta for
stencil clears
21:21 < Kayden> blorp only does color...
21:21 < Kayden> fast depth only does depth...
21:22 < Kayden> I don't know why we wouldn't be using blorp for stencil
21:23 < Kayden> erm
21:23 < Kayden> jekstrand: it looks like the GL driver is never using  
                blorp_clear_depth_stencil

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