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clAmdFft: why 3K case is much slower than 4K?

Question asked by gouse on Jun 13, 2013
Latest reply on Jun 13, 2013 by bragadeesh



I'm experiencing with clAmdFft and see that FFT of 3072x3072 image is way slower than 4096x4096 (ran with 'clAmdFft.Client.exe -g -o -x 4096 -y 4096 -p 20'):

  • 230ms for 3072x3072 image
  • 33ms for 4096x4096


What causes almost 8 times better performance for 1.7 more data? It should be related to 2^n, I guess. But which way?