[Bug 90734] glBufferSubData doesn't update the buffer

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=90734

            Bug ID: 90734
           Summary: glBufferSubData doesn't update the buffer
           Product: Mesa
           Version: git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/DRI/i965
          Assignee: idr at freedesktop.org
          Reporter: kaillasse91 at hotmail.fr
        QA Contact: intel-3d-bugs at lists.freedesktop.org

The behaviour of my application is very different with mesa and a Sandy bridge
HD2000 gpu.

Using INTEL_DEBUG=perf I see a lot of
'Using a blit copy to avoid stalling on glBufferSubData(6336, 6408) (0kb) to a
busy (0-72000) buffer object.'
with whatever the range I was updating is.

Getting the buffer back with glGetBufferSubData shows that the buffer is
sometimes not/impartially (?) updated.

Updating the whole buffer or forcing a sync with glFinish corrects the errors.

For info. :

void ShapeCollectionGl::updateBufferRange(int startIdx, int endIdx)
{
    glBindVertexArray(vao_);

    glBindBuffer(GL_ARRAY_BUFFER, vbo_);

    int offPos = shapesGl_[startIdx].offPos;
    int sizeData = shapesGl_[endIdx].offPos + shapesGl_[endIdx].pos.size() -
offPos;

    // glFinish() here solves the problem

    glBufferSubData(GL_ARRAY_BUFFER,
                    offPos * sizeof(VertexData),
                    sizeData * sizeof(VertexData),
                    &bufData_[offPos]);

    // reading the buffer back here with glGetBufferSubData shows the
difference

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo_);

    int offIdx = shapesGl_[startIdx].offIdx;
    int sizeIdx = shapesGl_[endIdx].offIdx + shapesGl_[endIdx].idx.size() -
offIdx;

    glBufferSubData(GL_ELEMENT_ARRAY_BUFFER,
                    offIdx * sizeof(GLuint),
                    sizeIdx * sizeof(GLuint),
                    &bufIdx_[offIdx]);

    glBindVertexArray(0);
}

00:02.0 VGA compatible controller [0300]: Intel Corporation 2nd Generation Core
Processor Family Integrated Graphics Controller [8086:0102] (rev 09) (prog-if
00 [VGA controller])

OpenGL core profile version string: 3.3 (Core Profile) Mesa 10.7.0-devel
(git-10aacf5 2015-05-28 trusty-oibaf-ppa)

Linux 4.0.4-040004-generic #201505171336 SMP Sun May 17 17:37:22 UTC 2015
x86_64 x86_64 x86_64 GNU/Linux

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