1
我正在嘗試使用posix_spawn而不是fork/exec來獲得一些性能增益。我目前的項目是用Python編寫的，所以我使用this Python綁定。此外，我嘗試了它的一些分支，之後我在Cython中編寫了自己的posix_spawn綁定（以消除一些依賴關係），但獲得了幾乎相同的結果。捕獲過程輸出時的Posix_spawn性能
當我只需要在不捕獲stdout/stderr的情況下運行進程時，確實有顯着的提速。但是當我確實需要它時（對於我的項目來說這是必要的），調用變得和fork/exec調用一樣慢。此外，它依賴於分配內存的數量與fork/exec相同。即使進程實際上沒有產生任何輸出，它也會發生 - 我檢查了/ bin/true。我仍然無法解釋這種行爲。對於fork/exec（通過子進程模塊），只要輸出不是太大，是否讀取過程輸出並沒有顯着差異。
這裏是我的測試腳本（進口並省略分析的代碼）不分配額外的內存
# test.py
def spawn_no_out(args):
command = args[0]
pid = posix_spawn(command, args)
status, rusage = exits(pid)
def spawn(args):
# Prepare pipes to capture stdout and stderr
stdout_read, stdout_write = os.pipe()
stderr_read, stderr_write = os.pipe()
fa = FileActions()
fa.add_dup2(stdout_write, 1)
fa.add_close(stdout_read)
fa.add_dup2(stderr_write, 2)
fa.add_close(stderr_read)
# Spawn the process
command = args[0]
pid = posix_spawn(command, args, file_actions=fa)
# Read and close file descriptors
os.close(stdout_write)
os.close(stderr_write)
status, rusage = exits(pid)
out = os.fdopen(stdout_read)
err = os.fdopen(stderr_read)
return out, err
def fork(args):
return Popen(args, stdout=PIPE, stderr=PIPE).communicate()
def fork_no_out(args):
return subprocess.call(args)
def run_benchmark(func, args, count):
for _ in xrange(count):
func(args)
print "%s: %ds" % (func.__name__, time.time() - start)
def main():
# Reads from stdout the number of process spawns and size of allocated memory
args = ["/bin/true"]
count = int(sys.argv[1]) if len(sys.argv) > 1 else 1000
mem_size = int(sys.argv[2]) if len(sys.argv) > 2 else 10000000
some_allocated_memory = range(mem_size)
for func in [spawn, spawn_no_out, fork, fork_no_out]:
run_benchmark(func, args, count)
if __name__ == "__main__":
main()
測試輸出：與1000萬個整數列表分配的內存
./test.py 10000 1
spawn: 34s
3754834 function calls (3754776 primitive calls) in 33.517 seconds
Ordered by: internal time, cumulative time
List reduced from 144 to 5 due to restriction
ncalls tottime percall cumtime percall filename:lineno(function)
10000 15.475 0.002 15.475 0.002 {posix.wait4}
10000 5.850 0.001 5.850 0.001 {_cffi__x2c5d2681xf492c09f.posix_spawn}
10000 3.217 0.000 12.750 0.001 /usr/local/lib/python2.7/dist-packages/posix_spawn-0.1-py2.7.egg/posix_spawn/_impl.py:75(posix_spawn)
10000 2.242 0.000 33.280 0.003 ./test.py:23(spawn)
660000 1.777 0.000 3.159 0.000 /usr/local/lib/python2.7/dist-packages/cffi/api.py:212(new)
spawn_no_out: 14s
3340013 function calls in 14.631 seconds
Ordered by: internal time, cumulative time
List reduced from 25 to 5 due to restriction
ncalls tottime percall cumtime percall filename:lineno(function)
10000 7.466 0.001 7.466 0.001 {posix.wait4}
10000 2.012 0.000 2.012 0.000 {_cffi__x2c5d2681xf492c09f.posix_spawn}
10000 1.658 0.000 6.994 0.001 /usr/local/lib/python2.7/dist-packages/posix_spawn-0.1-py2.7.egg/posix_spawn/_impl.py:75(posix_spawn)
650000 1.640 0.000 2.919 0.000 /usr/local/lib/python2.7/dist-packages/cffi/api.py:212(new)
650000 0.496 0.000 0.496 0.000 {_cffi_backend.newp}
fork: 40s
840094 function calls in 40.745 seconds
Ordered by: internal time, cumulative time
List reduced from 53 to 5 due to restriction
ncalls tottime percall cumtime percall filename:lineno(function)
10000 19.460 0.002 19.460 0.002 {posix.read}
10000 6.505 0.001 6.505 0.001 {posix.fork}
10081 4.667 0.000 4.667 0.000 {built-in method poll}
10000 2.773 0.000 30.190 0.003 /usr/lib/python2.7/subprocess.py:1187(_execute_child)
10000 0.814 0.000 32.996 0.003 /usr/lib/python2.7/subprocess.py:650(__init__)
fork_no_out: 38s
330013 function calls in 38.488 seconds
Ordered by: internal time, cumulative time
List reduced from 36 to 5 due to restriction
ncalls tottime percall cumtime percall filename:lineno(function)
10000 18.179 0.002 18.179 0.002 {posix.read}
10000 6.904 0.001 6.904 0.001 {posix.waitpid}
10000 6.613 0.001 6.613 0.001 {posix.fork}
10000 2.633 0.000 28.976 0.003 /usr/lib/python2.7/subprocess.py:1187(_execute_child)
10000 0.880 0.000 30.070 0.003 /usr/lib/python2.7/subprocess.py:650(__init__)
測試輸出（不得不減少通話次數）：
./test.py 1000 10000000
spawn: 20s
379834 function calls (379776 primitive calls) in 20.022 seconds
Ordered by: internal time, cumulative time
List reduced from 144 to 5 due to restriction
ncalls tottime percall cumtime percall filename:lineno(function)
1000 10.022 0.010 10.022 0.010 {posix.wait4}
1000 8.705 0.009 8.705 0.009 {_cffi__x2c5d2681xf492c09f.posix_spawn}
1000 0.334 0.000 9.412 0.009 /usr/local/lib/python2.7/dist-packages/posix_spawn-0.1-py2.7.egg/posix_spawn/_impl.py:75(posix_spawn)
1000 0.269 0.000 19.998 0.020 ./test.py:18(spawn)
66000 0.174 0.000 0.318 0.000 /usr/local/lib/python2.7/dist-packages/cffi/api.py:212(new)
spawn_no_out: 1s
334013 function calls in 1.480 seconds
Ordered by: internal time, cumulative time
List reduced from 25 to 5 due to restriction
ncalls tottime percall cumtime percall filename:lineno(function)
1000 0.755 0.001 0.755 0.001 {posix.wait4}
1000 0.198 0.000 0.198 0.000 {_cffi__x2c5d2681xf492c09f.posix_spawn}
1000 0.171 0.000 0.708 0.001 /usr/local/lib/python2.7/dist-packages/posix_spawn-0.1-py2.7.egg/posix_spawn/_impl.py:75(posix_spawn)
65000 0.167 0.000 0.298 0.000 /usr/local/lib/python2.7/dist-packages/cffi/api.py:212(new)
65000 0.050 0.000 0.050 0.000 {_cffi_backend.newp}
fork: 18s
84067 function calls in 18.554 seconds
Ordered by: internal time, cumulative time
List reduced from 53 to 5 due to restriction
ncalls tottime percall cumtime percall filename:lineno(function)
1000 9.399 0.009 9.399 0.009 {posix.read}
1000 7.815 0.008 7.815 0.008 {posix.fork}
1054 0.414 0.000 0.414 0.000 {built-in method poll}
1000 0.274 0.000 17.626 0.018 /usr/lib/python2.7/subprocess.py:1187(_execute_child)
1000 0.078 0.000 17.871 0.018 /usr/lib/python2.7/subprocess.py:650(__init__)
fork_no_out: 18s
33013 function calls in 18.732 seconds
Ordered by: internal time, cumulative time
List reduced from 36 to 5 due to restriction
ncalls tottime percall cumtime percall filename:lineno(function)
1000 9.467 0.009 9.467 0.009 {posix.read}
1000 8.020 0.008 8.020 0.008 {posix.fork}
1000 0.603 0.001 0.603 0.001 {posix.waitpid}
1000 0.280 0.000 17.910 0.018 /usr/lib/python2.7/subprocess.py:1187(_execute_child)
1000 0.072 0.000 18.000 0.018 /usr/lib/python2.7/subprocess.py:650(__init__)
Withou分析結果是一樣的。 正如我們所看到的，當我們在調用posix_spawn時和在沒有捕獲過程輸出的情況下，性能有很大差異（1.4s vs 20s！）。沒有額外的沉重電話 - posix.wait4只需要更多的時間。 我在這裏做錯了什麼？有人知道爲什麼會發生這種情況，以及如何爲posix_spawn獲得更好的性能？
P.S.在Linux Mint 17和CentOS 6.5上測試 - 結果相同。
UPDATE： 同樣的性能下降發生，即使我們通過空FileActions反對的posix_spawn，實際上並沒有閱讀標準輸出/標準錯誤：
def spawn(args):
command = args[0]
pid = posix_spawn(command, args, file_actions=FileActions())
status, rusage = exits(pid)
哇，吸 - 但是謝謝你找到解決方案。 –