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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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