进程数大于核心数的Python多进程行为

我正在尝试使用Python的 multiprocessing

我假设将进程设置为大于核心数没有任何好处。与假设相反,下面的实验代码说,即使进程数超过核心数(在我的例子中是4),计算时间也会减少。

from multiprocessing import Pool, cpu_count
import time
from datetime import datetime

cpu_count()
# 4

一项实验任务,大约需要0.5秒。

def f(x):
    time.sleep(0.5)
    return x*x

def execute_time(processes):
    t1 = datetime.now()
    with Pool(processes) as p:
        p.map(f, list(range(36)))
    t2 = datetime.now()
    return t2 - t1

for p in range(1, 25):
    t = execute_time(p)
    print(p, ":", t)

产生:

# 1 : 0:00:18.065411
# 2 : 0:00:10.051516
# 3 : 0:00:06.057016
# 4 : 0:00:04.562439
# 5 : 0:00:04.069810
# 6 : 0:00:03.173502
# 7 : 0:00:03.065977
# 8 : 0:00:03.082625
# 9 : 0:00:02.092880
# 10 : 0:00:02.090963
# 11 : 0:00:02.061613
# 12 : 0:00:01.704716
# 13 : 0:00:01.704880
# 14 : 0:00:01.615440
# 15 : 0:00:01.625117
# 16 : 0:00:01.621259
# 17 : 0:00:01.639741
# 18 : 0:00:01.236108
# 19 : 0:00:01.250113
# 20 : 0:00:01.255697
# 21 : 0:00:01.253459
# 22 : 0:00:01.260632
# 23 : 0:00:01.262124
# 24 : 0:00:01.247772