Michael Zucchi

 B.E. (Comp. Sys. Eng.)

  also known as zed
  & handle of notzed


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Saturday, 22 October 2011, 09:19

Its beaten me. For now.

I should've stayed outside in the sun today gardening - but curiosity got the better of me. I hope the (absolutely stunning) weather continues tomorrow, otherwise i've blown it on nothing ...

I tried working on the AMD performance of the Viola & Jones detector in socles: I tried a whole bunch of stuff, from copying the image tiles pre-scaled (as summed area table) to local memory, to completely re-arranging the data structures so they are workgroup aligned, to even trying the cpu single-thread-per-location version.

I got some minor improvement, the most being the copying the tile to local store and removing some of the calculations (since it doesn't need to scale the rects): but that only took a simple test case from about 25ms to 20ms. Barely really noticeable in my webcam test harness.

I think the problem is with the fact it has to read so much data for each single test. It requires 3-4 uint4's just to describe the test, and 8-12 uint texture lookups for the summed area table lookups. The cascade I have has ~6 400 regions to test grouped in ~3&nbsp000 features, and although most aren't tested it's just a lot of data. It's too much for constant memory for example.

With a fix to use the atomic counters AMD hardware provides at least it's now in the same order of magnitude as the nvidia hardware, but still 2-4x slower.

Maybe ... if the stages were broken up into smaller parts it could work more efficiently, but it does seem a pretty long shot to me as the problem remains with the sheer amount of stuff that needs to be loaded for each test.

Time probably better spent on something else.

Tagged opencl, socles.
OpenCL DCT Denoise | Ho hum.
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