TensorFlow中的SVD比numpy中的SVD慢

Question

I am observing that on my machine SVD in tensorflow is running significantly slower than in numpy. I have GTX 1080 GPU, and expecting SVD to be at least as fast as when running the code using CPU (numpy).

Environment Info

Operating System

lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 16.10
Release:    16.10
Codename:   yakkety

Installed version of CUDA and cuDNN:

ls -l /usr/local/cuda-8.0/lib64/libcud*
-rw-r--r-- 1 root      root    556000 Feb 22  2017 /usr/local/cuda-8.0/lib64/libcudadevrt.a
lrwxrwxrwx 1 root      root        16 Feb 22  2017 /usr/local/cuda-8.0/lib64/libcudart.so -> libcudart.so.8.0
lrwxrwxrwx 1 root      root        19 Feb 22  2017 /usr/local/cuda-8.0/lib64/libcudart.so.8.0 -> libcudart.so.8.0.61
-rwxr-xr-x 1 root      root    415432 Feb 22  2017 /usr/local/cuda-8.0/lib64/libcudart.so.8.0.61
-rw-r--r-- 1 root      root    775162 Feb 22  2017 /usr/local/cuda-8.0/lib64/libcudart_static.a
lrwxrwxrwx 1 voldemaro users       13 Nov  6  2016 /usr/local/cuda-8.0/lib64/libcudnn.so -> libcudnn.so.5
lrwxrwxrwx 1 voldemaro users       18 Nov  6  2016 /usr/local/cuda-8.0/lib64/libcudnn.so.5 -> libcudnn.so.5.1.10
-rwxr-xr-x 1 voldemaro users 84163560 Nov  6  2016 /usr/local/cuda-8.0/lib64/libcudnn.so.5.1.10
-rw-r--r-- 1 voldemaro users 70364814 Nov  6  2016 /usr/local/cuda-8.0/lib64/libcudnn_static.a

TensorFlow Setup

python -c "import tensorflow; print(tensorflow.__version__)"
I tensorflow/stream_executor/dso_loader.cc:135] successfully opened CUDA library libcublas.so.8.0 locally
I tensorflow/stream_executor/dso_loader.cc:135] successfully opened CUDA library libcudnn.so.5 locally
I tensorflow/stream_executor/dso_loader.cc:135] successfully opened CUDA library libcufft.so.8.0 locally
I tensorflow/stream_executor/dso_loader.cc:135] successfully opened CUDA library libcuda.so.1 locally
I tensorflow/stream_executor/dso_loader.cc:135] successfully opened CUDA library libcurand.so.8.0 locally
1.0.0

Code:

'''
Created on Sep 21, 2017

@author: voldemaro
'''
import numpy as np
import tensorflow as tf
import time;
import numpy.linalg as NLA;




N=1534;

svd_array = np.random.random_sample((N,N));
svd_array = svd_array.astype(complex);

specVar = tf.Variable(svd_array, dtype=tf.complex64);

[D2, E1,  E2] = tf.svd(specVar);

init_OP = tf.global_variables_initializer();

with tf.Session() as sess:
    # Initialize all tensorflow variables
    start = time.time();
    sess.run(init_OP);
    print 'initializing variables: {} s'.format(time.time()-start);

    start_time = time.time();
    [d, e1, e2]  = sess.run([D2, E1,  E2]);
    print("Tensorflow SVD ---: {} s" . format(time.time() - start_time));


# Equivalent numpy 
start = time.time();

u, s, v = NLA.svd(svd_array);   
print 'numpy SVD  ---: {} s'.format(time.time() - start);

Code Trace:

W tensorflow/core/platform/cpu_feature_guard.cc:45] The TensorFlow library wasn't compiled to use SSE4.2 instructions, but these are available on your machine and could speed up CPU computations.
W tensorflow/core/platform/cpu_feature_guard.cc:45] The TensorFlow library wasn't compiled to use AVX instructions, but these are available on your machine and could speed up CPU computations.
W tensorflow/core/platform/cpu_feature_guard.cc:45] The TensorFlow library wasn't compiled to use AVX2 instructions, but these are available on your machine and could speed up CPU computations.
W tensorflow/core/platform/cpu_feature_guard.cc:45] The TensorFlow library wasn't compiled to use FMA instructions, but these are available on your machine and could speed up CPU computations.
I tensorflow/stream_executor/cuda/cuda_gpu_executor.cc:910] successful NUMA node read from SysFS had negative value (-1), but there must be at least one NUMA node, so returning NUMA node zero
I tensorflow/core/common_runtime/gpu/gpu_device.cc:885] Found device 0 with properties: 
name: GeForce GTX 1080
major: 6 minor: 1 memoryClockRate (GHz) 1.7335
pciBusID 0000:01:00.0
Total memory: 7.92GiB
Free memory: 7.11GiB
I tensorflow/core/common_runtime/gpu/gpu_device.cc:906] DMA: 0 
I tensorflow/core/common_runtime/gpu/gpu_device.cc:916] 0:   Y 
I tensorflow/core/common_runtime/gpu/gpu_device.cc:975] Creating TensorFlow device (/gpu:0) -> (device: 0, name: GeForce GTX 1080, pci bus id: 0000:01:00.0)
initializing variables: 0.230546951294 s
Tensorflow SVD ---: 6.56117296219 s
numpy SVD  ---: 4.41714000702 s

Answer 1

GPU execution typically outperforms CPU only when parallelization is effective.

However, the parallelization of SVD algorithms is still subject to active research, meaning that no parallel version has been found yet to be vastly superior to the serial implementation.

Likely, the NumPy version is based on an extremely well optimized FORTRAN implementation, while I believe TensorFlow has its own C++ implementation, and apparently that is not as well optimized as the code that NumPy is calling.

EDIT : You may not be the first to observe the poorer performances of TensorFlow with SVD as compared to the FORTRAN implementations.

Answer 2

It looks like TensorFlow op implements gesvd whereas if you use MKL-enabled numpy/scipy (ie, if you use conda), it defaults to faster (but less numerically robust) gesdd

You can try comparing against gesvd in scipy:

from scipy import linalg
u0, s0, vt0 = linalg.svd(target0, lapack_driver="gesvd")

I've also experienced better results with MKL version so I've been using this helper class to transparently switch between TensorFlow and numpy versions of SVD, using tf.Variable to store results

You use it like this

result = SvdWrapper(tensor)
result.update()
sess.run([result.u, result.s, result.v])

Issue with more details on slowness: https://github.com/tensorflow/tensorflow/issues/13222