[Bug 106800] intelReadPixels: fallback to CPU mapping in PBO case for Z24S8 attachments

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=106800

            Bug ID: 106800
           Summary: intelReadPixels: fallback to CPU mapping in PBO case
                    for Z24S8 attachments
           Product: Mesa
           Version: git
          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: wickmarkus at web.de
        QA Contact: intel-3d-bugs at lists.freedesktop.org

Created attachment 139997
  --> https://bugs.freedesktop.org/attachment.cgi?id=139997&action=edit
Apitrace dump of citra showing the performance issue

Hi,

calling glReadPixels for the GL_DEPTH24_STENCIL8 attachment and the
GL_DEPTH_STENCIL / GL_UNSIGNED_INT_24_8 format seems to stall the GPU, even if
a PBO is bound. 92% of my CPU time is spend in intel_miptree_map.

I guess i965 lacks a copy shader for the tiled Z24S8 attachment to the linear
TBO buffer.

Tests was done on: Mesa DRI Intel(R) UHD Graphics 620 (Kabylake GT2)
and mesa: 4affeba1e9eb426a1ba13a3e8ced4673c4bb9b34

An apitrace dump which highlights this issue in the last frames is attached.

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