[笔记] 将numpy的操作转移到pytorch的tensor上运行可以加速

简单起见，仅实验了矩阵加法及广播操作，其他操作未实验。

目前结论是：

• 将numpy转为pytorch的tensor，可以加速(0.22s -> 0.12s)
• 如果将tensor加载到gpu上，能够加速更多(0.22s -> 0.0005s)，但是内存与显存的拷贝时间不容忽视

实验过的环境如下，结论都成立：

• Win10, 64 bit
• Ubuntu 18.04, 64 bit

但是据同事在Win10的Linux子系统下验证，据说将numpy转为pytorch的tensor后反而比前者更慢，怀疑是子系统实现产生的问题。

下面是验证流程。

import time
import numpy as np
import torch

print(torch.__version__)

1.4.0

def check_time(func, run_times=10):
    t = time.time()
    for i in range(run_times):
        func()
    print('avg time = %s sec' % ((time.time()-t)/run_times))

shape = (5000,5000)
a = np.ones(shape, dtype=np.float)
b = np.ones(shape, dtype=np.float)
k = np.ones((shape[0],1), dtype=np.float)

# - simple numpy ndarray plus

def test_np_1():
    c = a+b
    return c

check_time(test_np_1)

avg time = 0.21692438125610353 sec

# - simple numpy ndarray and broadcast

def test_np_2():
    c = a+b+k
    return c

check_time(test_np_2)

avg time = 0.45278918743133545 sec

# - use pytorch tensor

def test_torch_1():
    ta = torch.from_numpy(a)
    tb = torch.from_numpy(b)
    tc = ta+tb
    c = tc.numpy()
    return c

check_time(test_torch_1)

avg time = 0.11778402328491211 sec

# - use pytorch tensor and broadcast

def test_torch_2():
    ta = torch.from_numpy(a)
    tb = torch.from_numpy(b)
    tk = torch.from_numpy(k)
    tc = ta+tb+tk
    c = tc.numpy()
    return c

check_time(test_torch_2)

avg time = 0.2651021957397461 sec

# - check gpu

device = torch.device("cuda:0" if torch.cuda.is_available() else "cpu")
print(device)

ga = torch.from_numpy(a).float().to(device)
gb = torch.from_numpy(b).float().to(device)
gk = torch.from_numpy(k).float().to(device)

cuda:0

# - try tensor on gpu

def test_torch_cuda_1():
    ca = torch.from_numpy(a).float().to(device)
    cb = torch.from_numpy(b).float().to(device)
    cc = ca+cb
    c = cc.cpu().numpy()
    return c

check_time(test_torch_cuda_1)

avg time = 0.44039239883422854 sec

# - try tensor on gpu and broadcast

def test_torch_cuda_2():
    ca = torch.from_numpy(a).float().to(device)
    cb = torch.from_numpy(b).float().to(device)
    ck = torch.from_numpy(k).float().to(device)
    cc = ca+cb+ck
    c = cc.cpu().numpy()
    return c

check_time(test_torch_cuda_2)

avg time = 0.4477779150009155 sec

# - try tensor on gpu and broadcast, preload in gpu before call, and not copy to cpu after

def test_torch_cuda_3():
    cc = ga+gb+gk
    return cc

check_time(test_torch_cuda_3)

avg time = 0.0004986286163330078 sec