OpenGL Consuming ~50% GPU While Producing Nothing

Question

Overview

We have an image/movie viewer powered via Qt5 and OpenGL that performs well however, we find that the draw surface itself consumes a large swath of resources no matter what is playing, even when we strip down the shaders.

We've added timing (gl query timers) for all of our own, custom, tools and cannot locate the source of the additional performance draw. The draw times are quite low considering our use case (~7ms per frame).

This is for an image rendering app; So 2D textures only. We use 2 triangles to cover the viewport and then dynamically generate the fragment based on the input requirements. This is for the film industry in which we do many many things to an image in terms of color and composite.

Discovery

We've stripped down the fragment to near nothing:

#version 330 core
void main() {
    outColor = vec4(0.5, 0.0, 0.0, 1.0);
}

We've also disabled all PBO usage and have no uniform assignment. All timers read 0-1024ns for all of their commands (because all of our own gl commands are disabled)

The draw surface only calls paintGL, the Qt paint event for their OpenGL widget, once every ~42ms (24fps). Even with the simplicity of this, we use 70-80% of a GTX 1050 (resolution 3000x2000)

While this card is by no means a powerhouse, we are expecting to see less usage than that for something as simple as a solid color fragment. If we shrink the OpenGL window down to nothing, to only render the additional UI elements, we see ~5% usage. So our OpenGL surface that's doing next to nothing at a fixed frame rate is still consuming ~60-70% of the GPU for a reason we cannot determine.

Misc Info:

• https://forum.qt.io/topic/121179/high-gpu-usage-when-animating/2

Additional Testing

We've attempted an apitrace for the gl commands but nothing jumped out at us. This included turn off the blit from our render frame buffer to the windows' buffer. So realistically, all of these are internal Qt-driven OpenGL commands.

10008 glViewport(x = 0, y = 0, width = 3000, height = 1896)
10009 glClearColor(red = 0, green = 0, blue = 0, alpha = 1)
10010 glClear(mask = GL_COLOR_BUFFER_BIT)
10011 glBindVertexArray(array = 1)
10012 glUseProgram(program = 7)
10013 glBindBuffer(target = GL_ARRAY_BUFFER, buffer = 9)
10014 glVertexAttribPointer(index = 0, size = 3, type = GL_FLOAT, normalized = GL_TRUE, stride = 0, pointer = NULL)
10015 glEnableVertexAttribArray(index = 0)
10016 glBindBuffer(target = GL_ARRAY_BUFFER, buffer = 0)
10017 glBindBuffer(target = GL_ARRAY_BUFFER, buffer = 10)
10018 glVertexAttribPointer(index = 1, size = 2, type = GL_FLOAT, normalized = GL_TRUE, stride = 0, pointer = NULL)
10019 glEnableVertexAttribArray(index = 1)
10020 glBindBuffer(target = GL_ARRAY_BUFFER, buffer = 0)
10021 glBindTexture(target = GL_TEXTURE_2D, texture = 1)
10022 glBindBuffer(target = GL_ARRAY_BUFFER, buffer = 9)
10023 glVertexAttribPointer(index = 0, size = 3, type = GL_FLOAT, normalized = GL_TRUE, stride = 0, pointer = NULL)
10024 glEnableVertexAttribArray(index = 0)
10025 glBindBuffer(target = GL_ARRAY_BUFFER, buffer = 0)
10026 glUniformMatrix4fv(location = 4, count = 1, transpose = GL_FALSE, value = {1, 0, 0, 0, 0, 0.8016878, 0, 0, 0, 0, 1, 0, 0, 0.1476793, 0, 1})
10027 glBindBuffer(target = GL_ARRAY_BUFFER, buffer = 10)
10028 glVertexAttribPointer(index = 1, size = 2, type = GL_FLOAT, normalized = GL_TRUE, stride = 0, pointer = NULL)
10029 glEnableVertexAttribArray(index = 1)
10030 glBindBuffer(target = GL_ARRAY_BUFFER, buffer = 0)
10031 glUniform1i(location = 1, v0 = 0)
10032 glUniformMatrix3fv(location = 3, count = 1, transpose = GL_FALSE, value = {1, 0, 0, 0, 1, 0, 0, 0, 1})
10033 glDrawArrays(mode = GL_TRIANGLES, first = 0, count = 6)
10034 glBindTexture(target = GL_TEXTURE_2D, texture = 0)
10035 glPixelStorei(pname = GL_UNPACK_ROW_LENGTH, param = 3000)
10036 glBindTexture(target = GL_TEXTURE_2D, texture = 2)
10037 glTexSubImage2D(target = GL_TEXTURE_2D, level = 0, xoffset = 0, yoffset = 48, width = 3000, height = 1520, format = GL_RGBA, type = GL_UNSIGNED_BYTE, pixels = blob(18240000))
10038 glPixelStorei(pname = GL_UNPACK_ROW_LENGTH, param = 0)
10039 glEnable(cap = GL_BLEND)
10040 glBlendFuncSeparate(sfactorRGB = GL_ONE, dfactorRGB = GL_ONE_MINUS_SRC_ALPHA, sfactorAlpha = GL_ONE, dfactorAlpha = GL_ONE)
10041 glBindTexture(target = GL_TEXTURE_2D, texture = 2)
10042 glBindBuffer(target = GL_ARRAY_BUFFER, buffer = 9)
10043 glVertexAttribPointer(index = 0, size = 3, type = GL_FLOAT, normalized = GL_TRUE, stride = 0, pointer = NULL)
10044 glEnableVertexAttribArray(index = 0)
10045 glBindBuffer(target = GL_ARRAY_BUFFER, buffer = 0)
10046 glUniformMatrix4fv(location = 4, count = 1, transpose = GL_FALSE, value = {1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1})
10047 glBindBuffer(target = GL_ARRAY_BUFFER, buffer = 10)
10048 glVertexAttribPointer(index = 1, size = 2, type = GL_FLOAT, normalized = GL_TRUE, stride = 0, pointer = NULL)
10049 glEnableVertexAttribArray(index = 1)
10050 glBindBuffer(target = GL_ARRAY_BUFFER, buffer = 0)
10051 glUniform1i(location = 1, v0 = 1)
10052 glUniformMatrix3fv(location = 3, count = 1, transpose = GL_FALSE, value = {1, 0, 0, 0, -1, 0, 0, 1, 1})
10053 glDrawArrays(mode = GL_TRIANGLES, first = 0, count = 6)
10054 glBindTexture(target = GL_TEXTURE_2D, texture = 0)
10055 glDisable(cap = GL_BLEND)
10056 glUseProgram(program = 0)
10057 glBindVertexArray(array = 0)
10058 wglSwapBuffers(hdc = 0xffffffff86011399) = TRUE

Any ideas would be excellent. I'm also happy to provide more information if required.