Tensorflow中使用cpu和gpu有什么区别

import tensorflow as tf
import timeit
import numpy as np
import matplotlib.pyplot as plt
def cpu_run(num):
  with tf.device('/cpu:0'):
    cpu_a=tf.random.normal([1,num])
    cpu_b=tf.random.normal([num,1])
    c=tf.matmul(cpu_a,cpu_b)
  return c
def gpu_run(num):
  with tf.device('/gpu:0'):
    gpu_a=tf.random.normal([1,num])
    gpu_b=tf.random.normal([num,1])
    c=tf.matmul(gpu_a,gpu_b)
  return c
k=10
m=7
cpu_result=np.arange(m,dtype=np.float32)
gpu_result=np.arange(m,dtype=np.float32)
x_time=np.arange(m)
for i in range(m):
  k=k*10
  x_time[i]=k
  cpu_str='cpu_run('+str(k)+')'
  gpu_str='gpu_run('+str(k)+')'
  #print(cpu_str)
  cpu_time=timeit.timeit(cpu_str,'from __main__ import cpu_run',number=10)
  gpu_time=timeit.timeit(gpu_str,'from __main__ import gpu_run',number=10)
  # 正式计算10次，取平均时间
  cpu_time=timeit.timeit(cpu_str,'from __main__ import cpu_run',number=10)
  gpu_time=timeit.timeit(gpu_str,'from __main__ import gpu_run',number=10)
  cpu_result[i]=cpu_time
  gpu_result[i]=gpu_time
print(cpu_result)
print(gpu_result)
fig, ax = plt.subplots()
ax.set_xscale("log")
ax.set_adjustable("datalim")
ax.plot(x_time,cpu_result)
ax.plot(x_time,gpu_result)
ax.grid()
plt.draw()
plt.show()