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glGenerateMipmap() very slow on Samsung Galaxy SII

bert bert
Note: This was originally posted on 15th February 2012 at http://forums.arm.com

Hi,
I'm currently doing some GPGPU on the Samsung Galaxy SII (Mali-400 MP). For that I need to generate a mipmap from a texture that has been rendered to via a FBO. Unfortunately glGenerateMipmap() appears to be very slow on the device. It takes about 90 milliseconds to generate a mipmap for a 512x512 RGBA8888 texture. Since I also tried the same code on other Android devices, where this function works much faster (about 2 milliseconds), this slowdown really puzzles me. Am I doing something wrong or missing something here? Can anyone provide example code for this case working on a MALI device?

Here are the relevant parts of my code:

glGenTextures(1, &texId);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, texId);

// Allocate graphics memory.
glTexImage2D(GL_TEXTURE_2D, 0, format, cols, rows, 0, format, type, NULL);
// Allocate memory for mipmap.
glGenerateMipmap(GL_TEXTURE_2D);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

// Create off-screen framebuffer object and attach the texture to it.
glGenFramebuffers(1, &fboId);
glBindFramebuffer(GL_FRAMEBUFFER, fboId);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texId, 0);

// Now render to that texture
...

// Generate MIP map.
glBindTexture(GL_TEXTURE_2D, texId);
glGenerateMipmap(GL_TEXTURE_2D);
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  • Note: This was originally posted on 21st February 2012 at http://forums.arm.com

    Hey Pete,

    thanks for looking into this.

    On all devices GL_GENERATE_MIPMAP_HINT is 0x1100 (GL_DONT_CARE). I tried  changing it to GL_NICEST and GL_FASTEST on the Mali device before  generating the mipmap, but that did not change anything.

    Yes, I need to mipmap the input texture (which represents a frame of a  camera stream) in every frame and also I am sort of rendering it by  extracting SURF features at interest point positions (those are  scale-space positions, hence I need a mipmap) into another texture.

    Timing the OpenGL ES calls is quite tedious. Currently I'm timing my  whole pipeline for about 100-300 iterations and average the resulting  values. To measure the time of a certain step, I reduce my pipeline step  by step, and estimate the time for each step by substracting. I also  measured the call to glGenerateMipmap() directly by wrapping the timing  functions around it, but that yielded the same results.
    However, actually I'm not 100% sure that what I'm measuring there is  really what I think it is. But that's a problem with OpenGL ES: it's  hard to measure anything more fine-grained than a whole rendering cycle.

    Greet, Bert
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  • Note: This was originally posted on 21st February 2012 at http://forums.arm.com

    Hey Pete,

    thanks for looking into this.

    On all devices GL_GENERATE_MIPMAP_HINT is 0x1100 (GL_DONT_CARE). I tried  changing it to GL_NICEST and GL_FASTEST on the Mali device before  generating the mipmap, but that did not change anything.

    Yes, I need to mipmap the input texture (which represents a frame of a  camera stream) in every frame and also I am sort of rendering it by  extracting SURF features at interest point positions (those are  scale-space positions, hence I need a mipmap) into another texture.

    Timing the OpenGL ES calls is quite tedious. Currently I'm timing my  whole pipeline for about 100-300 iterations and average the resulting  values. To measure the time of a certain step, I reduce my pipeline step  by step, and estimate the time for each step by substracting. I also  measured the call to glGenerateMipmap() directly by wrapping the timing  functions around it, but that yielded the same results.
    However, actually I'm not 100% sure that what I'm measuring there is  really what I think it is. But that's a problem with OpenGL ES: it's  hard to measure anything more fine-grained than a whole rendering cycle.

    Greet, Bert
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