softmax_mask_fuse_upper_triangle

paddle.incubate. softmax_mask_fuse_upper_triangle ( x ) [source]

Do a masked softmax on x, which will always mask upper triangle part of x.

This is designed for speeding up GPT kind Transformer structure. Used for reducing operation such as: tmp = x + mask, out = softmax(tmp), where the mask is always be an upper triangle matrix. The equation is:

\[out = softmax(LowerTriangular(x))\]
Note:

This API only supports GPU.

Parameters

x (4-D Tensor) – The input tensor, should be in 4D shape, it’s data type should be float16, float32 The fourth dimension of x must be larger or equal to 32 and less then 8192. The third dimension of x must be same with the fourth dimension of x.

Returns

4-D Tensor. A location into which the result is stored. It’s dimension is 4D. Has same dimension with x.

Examples

# required: gpu
import paddle
import paddle.incubate as incubate

x = paddle.rand((1, 1, 32, 32))

rst = incubate.softmax_mask_fuse_upper_triangle(x)
# [[[[1.        , 0.        , 0.        , ..., 0., 0., 0.],
#    [0.45324376, 0.54675621, 0.        , ..., 0., 0., 0.],
#    [0.32674268, 0.28156221, 0.39169508, ..., 0., 0., 0.]
#     ... ]]]