我使用 keras + theano 从 NVidia TK1 上的 VGG 预训练模型预测标签。
在预测中，我从 CPU 获得的预测时间比从 GPU 获得的预测时间更快。如果我没记错的话，预测还涉及大量重复的数字运算。我不明白为什么CPU会在这里变慢。
有人有很好的解释吗？
GPU 详细信息行：Using gpu device 0: GK20A (CNMeM is enabled with initial size: 75.0% of memory, cuDNN Version is too old. Update to v5, was 2000.)
这是预测的分析结果：
Class
---
<% time> <sum %> <apply time> <time per call> <type> <#call> <#apply> <Class name>
39.5% 39.5% 0.019s 6.42e-03s C 3 3 theano.sandbox.cuda.blas.GpuDot22
24.8% 64.3% 0.012s 6.04e-03s C 2 2 theano.sandbox.cuda.blas.GpuCorrMM
16.4% 80.8% 0.008s 1.33e-03s C 6 6 theano.sandbox.cuda.basic_ops.GpuElemwise
7.8% 88.5% 0.004s 1.89e-03s C 2 2 theano.sandbox.cuda.blas.GpuDownsampleFactorMax
4.2% 92.7% 0.002s 2.03e-03s C 1 1 theano.sandbox.rng_mrg.GPU_mrg_uniform
3.8% 96.4% 0.002s 4.57e-04s C 4 4 theano.sandbox.cuda.basic_ops.GpuContiguous
2.3% 98.8% 0.001s 5.66e-04s C 2 2 theano.sandbox.cuda.basic_ops.GpuFromHost
0.5% 99.3% 0.000s 2.51e-04s C 1 1 theano.sandbox.cuda.nnet.GpuSoftmaxWithBias
0.5% 99.8% 0.000s 2.39e-04s C 1 1 theano.sandbox.cuda.basic_ops.HostFromGpu
0.1% 99.8% 0.000s 1.37e-05s C 3 3 theano.sandbox.cuda.basic_ops.GpuReshape
0.0% 99.9% 0.000s 9.54e-06s C 2 2 theano.sandbox.cuda.basic_ops.GpuSubtensor
0.0% 99.9% 0.000s 4.35e-06s C 4 4 theano.tensor.elemwise.Elemwise
0.0% 99.9% 0.000s 5.01e-06s C 2 2 theano.sandbox.cuda.basic_ops.GpuDimShuffle
0.0% 100.0% 0.000s 3.26e-06s C 3 3 theano.compile.ops.Shape_i
0.0% 100.0% 0.000s 4.53e-06s C 2 2 theano.tensor.opt.MakeVector
0.0% 100.0% 0.000s 5.96e-06s C 1 1 theano.tensor.elemwise.Prod
0.0% 100.0% 0.000s 3.10e-06s C 1 1 theano.tensor.elemwise.DimShuffle
... (remaining 0 Classes account for 0.00%(0.00s) of the runtime)
Ops
---
<% time> <sum %> <apply time> <time per call> <type> <#call> <#apply> <Op name>
39.5% 39.5% 0.019s 6.42e-03s C 3 3 GpuDot22
24.8% 64.3% 0.012s 6.04e-03s C 2 2 GpuCorrMM{valid, (1, 1)}
11.2% 75.5% 0.005s 1.36e-03s C 4 4 GpuElemwise{Composite{(i0 * ((i1 + i2) + Abs((i1 + i2))))}}[(0, 1)]
7.8% 83.3% 0.004s 1.89e-03s C 2 2 GpuDownsampleFactorMax{(2, 2),True}
4.2% 87.4% 0.002s 2.03e-03s C 1 1 GPU_mrg_uniform{CudaNdarrayType(float32, 4D),inplace}
3.8% 91.2% 0.002s 4.57e-04s C 4 4 GpuContiguous
2.9% 94.1% 0.001s 1.43e-03s C 1 1 GpuElemwise{Composite{Cast{float32}(LT(i0, i1))}}[(0, 0)]
2.3% 96.5% 0.001s 5.66e-04s C 2 2 GpuFromHost
2.3% 98.8% 0.001s 1.12e-03s C 1 1 GpuElemwise{Composite{Switch(i0, (i1 * i2 * i3), i2)}}[(0, 2)]
0.5% 99.3% 0.000s 2.51e-04s C 1 1 GpuSoftmaxWithBias
0.5% 99.8% 0.000s 2.39e-04s C 1 1 HostFromGpu
0.1% 99.8% 0.000s 1.60e-05s C 2 2 GpuReshape{4}
0.0% 99.9% 0.000s 9.54e-06s C 2 2 GpuSubtensor{::, ::, ::int64, ::int64}
0.0% 99.9% 0.000s 5.01e-06s C 2 2 GpuDimShuffle{x,0}
0.0% 99.9% 0.000s 4.53e-06s C 2 2 MakeVector{dtype='int64'}
0.0% 99.9% 0.000s 9.06e-06s C 1 1 GpuReshape{2}
0.0% 99.9% 0.000s 4.17e-06s C 2 2 Elemwise{Composite{((i0 + ((i1 + i2) // i3)) // i3)}}[(0, 2)]
0.0% 100.0% 0.000s 5.96e-06s C 1 1 Prod{acc_dtype=int64}
0.0% 100.0% 0.000s 5.96e-06s C 1 1 Elemwise{Cast{float32}}
0.0% 100.0% 0.000s 5.01e-06s C 1 1 Shape_i{0}
... (remaining 4 Ops account for 0.02%(0.00s) of the runtime)
Apply
------
<% time> <sum %> <apply time> <time per call> <#call> <id> <Apply name>
36.4% 36.4% 0.018s 1.77e-02s 1 33 GpuDot22(GpuReshape{2}.0, dense_5_W)
15.7% 52.1% 0.008s 7.64e-03s 1 18 GpuCorrMM{valid, (1, 1)}(GpuContiguous.0, GpuContiguous.0)
9.1% 61.2% 0.004s 4.44e-03s 1 28 GpuCorrMM{valid, (1, 1)}(GpuContiguous.0, GpuContiguous.0)
5.7% 66.9% 0.003s 2.76e-03s 1 25 GpuDownsampleFactorMax{(2, 2),True}(GpuElemwise{Composite{(i0 * ((i1 + i2) + Abs((i1 + i2))))}}[(0, 1)].0)
4.2% 71.0% 0.002s 2.03e-03s 1 20 GPU_mrg_uniform{CudaNdarrayType(float32, 4D),inplace}(<CudaNdarrayType(float32, vector)>, MakeVector{dtype='int64'}.0)
3.6% 74.6% 0.002s 1.74e-03s 1 34 GpuElemwise{Composite{(i0 * ((i1 + i2) + Abs((i1 + i2))))}}[(0, 1)](CudaNdarrayConstant{[[ 0.5]]}, GpuDot22.0, GpuDimShuffle{x,0}.0)
3.2% 77.8% 0.002s 1.54e-03s 1 22 GpuElemwise{Composite{(i0 * ((i1 + i2) + Abs((i1 + i2))))}}[(0, 1)](CudaNdarrayConstant{[[[[ 0.5]]]]}, GpuCorrMM{valid, (1, 1)}.0, GpuReshape{4}.0)
2.9% 80.7% 0.001s 1.43e-03s 1 23 GpuElemwise{Composite{Cast{float32}(LT(i0, i1))}}[(0, 0)](GPU_mrg_uniform{CudaNdarrayType(float32, 4D),inplace}.1, CudaNdarrayConstant{[[[[ 0.80000001]]]]})
2.7% 83.4% 0.001s 1.29e-03s 1 36 GpuElemwise{Composite{(i0 * ((i1 + i2) + Abs((i1 + i2))))}}[(0, 1)](CudaNdarrayConstant{[[ 0.5]]}, GpuDot22.0, GpuDimShuffle{x,0}.0)
2.3% 85.7% 0.001s 1.12e-03s 1 31 GpuElemwise{Composite{Switch(i0, (i1 * i2 * i3), i2)}}[(0, 2)](GpuFromHost.0, CudaNdarrayConstant{[[[[ 1.25]]]]}, GpuDownsampleFactorMax{(2, 2),True}.0, GpuElemwise{Composite{Cast{float32}(LT(i0, i1))}}[(0, 0)].0)
2.2% 87.8% 0.001s 1.06e-03s 1 14 GpuContiguous(GpuSubtensor{::, ::, ::int64, ::int64}.0)
2.2% 90.0% 0.001s 1.06e-03s 1 35 GpuDot22(GpuElemwise{Composite{(i0 * ((i1 + i2) + Abs((i1 + i2))))}}[(0, 1)].0, dense_6_W)
2.1% 92.1% 0.001s 1.01e-03s 1 30 GpuDownsampleFactorMax{(2, 2),True}(GpuElemwise{Composite{(i0 * ((i1 + i2) + Abs((i1 + i2))))}}[(0, 1)].0)
2.0% 94.1% 0.001s 9.61e-04s 1 3 GpuFromHost(convolution2d_input_1)
1.8% 95.9% 0.001s 8.71e-04s 1 29 GpuElemwise{Composite{(i0 * ((i1 + i2) + Abs((i1 + i2))))}}[(0, 1)](CudaNdarrayConstant{[[[[ 0.5]]]]}, GpuCorrMM{valid, (1, 1)}.0, GpuReshape{4}.0)
1.6% 97.4% 0.001s 7.58e-04s 1 15 GpuContiguous(GpuSubtensor{::, ::, ::int64, ::int64}.0)
1.0% 98.4% 0.000s 4.72e-04s 1 37 GpuDot22(GpuElemwise{Composite{(i0 * ((i1 + i2) + Abs((i1 + i2))))}}[(0, 1)].0, dense_7_W)
0.5% 98.9% 0.000s 2.51e-04s 1 38 GpuSoftmaxWithBias(GpuDot22.0, dense_7_b)
0.5% 99.4% 0.000s 2.39e-04s 1 39 HostFromGpu(GpuSoftmaxWithBias.0)
0.3% 99.8% 0.000s 1.70e-04s 1 19 GpuFromHost(Elemwise{Cast{float32}}.0)
... (remaining 20 Apply instances account for 0.25%(0.00s) of the runtime)