Theano GPU 计算比 numpy 慢

Question

我正在学习使用 theano。我想通过为其中的每个元素计算二进制 TF-IDF 来填充术语文档矩阵（一个 numpy 稀疏矩阵）：

import theano
import theano.tensor as T
import numpy as np
from time import perf_counter

def tfidf_gpu(appearance_in_documents,num_documents,document_words):
    start = perf_counter()
    APP = T.scalar('APP',dtype='int32')
    N = T.scalar('N',dtype='int32')
    SF = T.scalar('S',dtype='int32')
    F = (T.log(N)-T.log(APP)) / SF
    TFIDF = theano.function([N,APP,SF],F)
    ret = TFIDF(num_documents,appearance_in_documents,document_words)
    end = perf_counter()
    print("\nTFIDF_GPU ",end-start," secs.")
    return ret

def tfidf_cpu(appearance_in_documents,num_documents,document_words):
    start = perf_counter()
    tfidf = (np.log(num_documents)-np.log(appearance_in_documents))/document_words
    end = perf_counter()
    print("TFIDF_CPU ",end-start," secs.\n")
    return tfidf

但是numpy版本比theano实现快很多：

Progress 1/43
TFIDF_GPU  0.05702276699594222  secs.
TFIDF_CPU  1.454801531508565e-05  secs.

Progress 2/43
TFIDF_GPU  0.023830442980397493  secs.
TFIDF_CPU  1.1073017958551645e-05  secs.

Progress 3/43
TFIDF_GPU  0.021920352999586612  secs.
TFIDF_CPU  1.0738993296399713e-05  secs.

Progress 4/43
TFIDF_GPU  0.02303648801171221  secs.
TFIDF_CPU  1.1675001587718725e-05  secs.

Progress 5/43
TFIDF_GPU  0.02359767400776036  secs.
TFIDF_CPU  1.4385004760697484e-05  secs.

....

我了解到这可能是开销造成的，对于小操作可能会降低性能。

是我的代码不好还是我应该避免使用 GPU 因为开销？

Answer 1

问题是你每次都在编译你的 Theano 函数。编译需要时间。尝试像这样传递编译后的函数：

def tfidf_gpu(appearance_in_documents,num_documents,document_words,TFIDF):
    start = perf_counter()
    ret = TFIDF(num_documents,appearance_in_documents,document_words)
    end = perf_counter()
    print("\nTFIDF_GPU ",end-start," secs.")
    return ret

APP = T.scalar('APP',dtype='int32')
N = T.scalar('N',dtype='int32')
SF = T.scalar('S',dtype='int32')
F = (T.log(N)-T.log(APP)) / SF
TFIDF = theano.function([N,APP,SF],F)

tfidf_gpu(appearance_in_documents,num_documents,document_words,TFIDF)

另外，您的 TFIDF 任务是带宽密集型任务。 Theano 和一般的 GPU 最适合计算密集型任务。

当前任务将数据传入 GPU 并返回的开销相当大，因为最终您需要读取每个元素 O(1) 次。但是如果你想做更多的计算，使用 GPU 是有意义的。

Theano GPU 计算比 numpy 慢

Theano GPU calculation slower than numpy

python

numpy

theano

tf-idf