libtorch does not initialize OpenMP/MKL by default #20156
Description
I find that matrix multiplication is slower in C++ API, so I write the same code in C++ and python and record their execution times, code is as following:
C++:
#include<torch/torch.h>
#include<iostream>
#include <chrono>
int main(){
torch::Tensor tensor = torch::randn({2708, 1433});
torch::Tensor weight = torch::randn({1433, 16});
auto start = std::chrono::high_resolution_clock::now();
tensor.mm(weight);
auto end = std::chrono::high_resolution_clock::now();
std::cout<< "C++ Operation Time(s) " << std::chrono::duration<double>(end - start).count() << "s" << std::endl;
return 0;
}
Result:
C++ Operation Time(s) 0.082496s
python:
import torch
import torch.nn as nn
import torch.nn.functional as F
tensor = torch.randn(2708, 1433)
weight = torch.randn(1433, 16)
t0 = time.time()
tensor.mm(weight)
t1 = time.time()
print("Python Operation Time(s) {:.4f}".format(t1 - t0))
Result:
Python Operation Time(s) 0.0114
Testing Environment:
ubuntu 16.04
gcc version 5.4.0
python version 3.7.3
pytorch version 1.0.1
It's not a small difference, why is it happen???