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@chengduoZH chengduoZH commented Apr 24, 2018

There is a lack of synchronization in reduceSum, so the results of it have some randomness when the thread block excess 256. But the reason of why randomness doesn't happen when thread block is less than 256 is not clear.


@chengduoZH chengduoZH requested a review from panyx0718 April 24, 2018 00:44
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Can you add your test as well?

@chengduoZH chengduoZH force-pushed the fix_elementwise_gradient branch from 612685e to 5b345d1 Compare April 24, 2018 02:38
@chengduoZH chengduoZH force-pushed the fix_elementwise_gradient branch from 5b345d1 to d06c79c Compare April 24, 2018 02:49
@chengduoZH chengduoZH requested a review from qingqing01 April 24, 2018 03:30
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atol=2.0 ? So large?

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The process of getting gradient involves accumulative operation and the shape of input is too large, x.shape = [2,32,220,220], y.shape = [32], so the diff of the result between Python and C++(CUDA) is bigger.

Python result
array([96771.625, 96801.26 , 96760.63 , 96893.32 , 96946.375, 96911.95 ,
       96837.16 , 96716.88 , 96931.305, 96746.445, 96781.81 , 96827.22 ,
       97108.19 , 96866.8  , 96894.17 , 96776.36 , 96720.61 , 96992.8  ,
       96641.664, 96772.305, 96698.16 , 96675.64 , 96805.86 , 96710.6  ,
       96733.37 , 96858.41 , 96771.516, 97033.516, 96820.48 , 96726.09 ,
       96784.66 , 96740.76 ], dtype=float32)

C++ result
array([96771.1  , 96801.05 , 96761.125, 96892.69 , 96946.73 , 96910.93 ,
       96837.516, 96716.27 , 96930.99 , 96748.18 , 96781.41 , 96828.016,
       97108.17 , 96866.62 , 96893.836, 96775.74 , 96720.98 , 96992.24 ,
       96642.36 , 96771.14 , 96698.195, 96675.055, 96805.88 , 96711.305,
       96732.086, 96858.97 , 96770.734, 97033.92 , 96819.95 , 96725.72 ,
       96784.35 , 96740.76 ], dtype=float32)

CUDA result
array([96738.2  , 96891.58 , 96752.25 , 96972.39 , 96706.016, 96755.234,
       96731.42 , 96850.01 , 97060.125, 96790.375, 96587.12 , 96833.305,
       96709.3  , 96703.7  , 96842.61 , 96727.95 , 96966.586, 96791.33 ,
       97077.234, 96715.03 , 96850.26 , 96898.47 , 96780.97 , 96839.516,
       96835.61 , 96600.41 , 96517.08 , 96787.58 , 96758.37 , 96555.484,
       96882.94 , 96578.2  ], dtype=float32)

So the max diff between Python result and C++ result is 1.28125, the max diff between Python result and CUDA result is 0.015625.

@chengduoZH chengduoZH force-pushed the fix_elementwise_gradient branch from e2f89a1 to 3623f02 Compare April 24, 2018 05:44
@chengduoZH chengduoZH merged commit bfbbe19 into PaddlePaddle:develop Apr 24, 2018
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fix #10122

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