PyPy比CPython慢得多

2018-06-04 16:33:53

我一直在测试我制作的缓存系统。它的目的是加速Django Web应用程序。它将所有内容存储在内存中。根据cProfile，在我的测试中，大部分时间都花费在QuerySet._clone（）中，结果是效率非常低（实际上并不奇怪）。

我对使用PyPy加快速度寄予厚望。我有一台64位机器。然而，在安装了所有必需的库之后，PyPy编译后的代码运行速度比普通Python代码慢2.5倍左右，我不知道该如何解决它。代码是CPU绑定的（绝对没有数据库查询，所以IO绑定不是一个选项）。一次测试运行约10秒钟，所以我认为它应该足以让JIT开始使用。我正在使用PyPy 1.5。一个说明 - 我没有自己编译源代码，只是下载了一个64位的linux版本。

我想知道CPU密集型代码在PyPy下实际运行速度有多频繁。有没有希望有什么错误我可以做，这将阻止PyPy运行在最佳状态。

编辑

精确的cPython输出：

PyPy 1.5：

    3439146 function calls (3218654 primitive calls) in 19.094 seconds

    Ordered by: cumulative time

    ncalls  tottime  percall  cumtime  percall filename:lineno(function)
       2/1    0.000    0.000   18.956   18.956 <string>:1(<module>)
       2/1    0.000    0.000   18.956   18.956 /path/to/my/project/common/integrity/models/transactions.py:200(newfn)
       2/1    0.000    0.000   18.956   18.956 /path/to/my/project/common/integrity/models/transactions.py:134(recur)
       2/1    0.000    0.000   18.956   18.956 /usr/local/pypy/site-packages/django/db/transaction.py:210(inner)
       2/1    0.172    0.086   18.899   18.899 /path/to/my/project/common/integrity/tests/optimization.py:369(func_cached)
      9990    0.122    0.000   18.632    0.002 /usr/local/pypy/site-packages/django/db/models/manager.py:131(get)
      9990    0.127    0.000   16.638    0.002 /path/to/my/project/common/integrity/models/cache.py:1068(get)
      9990    0.073    0.000   12.478    0.001 /usr/local/pypy/site-packages/django/db/models/query.py:547(filter)
      9990    0.263    0.000   12.405    0.001 /path/to/my/project/common/integrity/models/cache.py:1047(_filter_or_exclude)
      9990    0.226    0.000   12.096    0.001 /usr/local/pypy/site-packages/django/db/models/query.py:561(_filter_or_exclude)
      9990    0.187    0.000    8.383    0.001 /path/to/my/project/common/integrity/models/cache.py:765(_clone)
      9990    0.212    0.000    7.662    0.001 /usr/local/pypy/site-packages/django/db/models/query.py:772(_clone)
      9990    1.025    0.000    7.125    0.001 /usr/local/pypy/site-packages/django/db/models/sql/query.py:226(clone)
129942/49972  1.674    0.000    6.021    0.000 /usr/local/pypy/lib-python/2.7/copy.py:145(deepcopy)
140575/110605 0.120    0.000    4.066    0.000 {len}
      9990    0.182    0.000    3.972    0.000 /usr/local/pypy/site-packages/django/db/models/query.py:74(__len__)
     19980    0.260    0.000    3.777    0.000 /path/to/my/project/common/integrity/models/cache.py:1062(iterator)
      9990    0.255    0.000    3.154    0.000 /usr/local/pypy/site-packages/django/db/models/sql/query.py:1149(add_q)
      9990    0.210    0.000    3.073    0.000 /path/to/my/project/common/integrity/models/cache.py:973(_query)
      9990    0.371    0.000    2.316    0.000 /usr/local/pypy/site-packages/django/db/models/sql/query.py:997(add_filter)
      9990    0.364    0.000    2.168    0.000 /path/to/my/project/common/integrity/models/cache.py:892(_deduct)
29974/9994    0.448    0.000    2.078    0.000 /usr/local/pypy/lib-python/2.7/copy.py:234(_deepcopy_tuple)
     19990    0.362    0.000    2.065    0.000 /path/to/my/project/common/integrity/models/cache.py:566(__init__)
     10000    0.086    0.000    1.874    0.000 /path/to/my/project/common/integrity/models/cache.py:1090(get_query_set)
     19990    0.269    0.000    1.703    0.000 /usr/local/pypy/site-packages/django/db/models/query.py:31(__init__)
      9990    0.122    0.000    1.643    0.000 /path/to/my/project/common/integrity/models/cache.py:836(_deduct_recur)
     19980    0.274    0.000    1.636    0.000 /usr/local/pypy/site-packages/django/utils/tree.py:55(__deepcopy__)
      9990    0.607    0.000    1.458    0.000 /path/to/my/project/common/integrity/models/cache.py:789(_deduct_local)
     10020    0.633    0.000    1.437    0.000 /usr/local/pypy/site-packages/django/db/models/sql/query.py:99(__init__)
    129942    0.841    0.000    1.191    0.000 /usr/local/pypy/lib-python/2.7/copy.py:267(_keep_alive)
 9994/9992    0.201    0.000    1.019    0.000 /usr/local/pypy/lib-python/2.7/copy.py:306(_reconstruct)

Python 2.7：

   3326403 function calls (3206359 primitive calls) in 12.430 CPU seconds

   Ordered by: cumulative time

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
        1    0.000    0.000   12.457   12.457 <string>:1(<module>)
        1    0.000    0.000   12.457   12.457 /path/to/my/project/common/integrity/models/transactions.py:200(newfn)
        1    0.000    0.000   12.457   12.457 /path/to/my/project/common/integrity/models/transactions.py:134(recur)
        1    0.000    0.000   12.457   12.457 /usr/local/lib/python2.7/dist-packages/django/db/transaction.py:210(inner)
        1    0.000    0.000   12.457   12.457 /path/to/my/project/common/integrity/models/transactions.py:165(recur2)
        1    0.089    0.089   12.450   12.450 /path/to/my/project/common/integrity/tests/optimization.py:369(func_cached)
     9990    0.198    0.000   12.269    0.001 /usr/local/lib/python2.7/dist-packages/django/db/models/manager.py:131(get)
     9990    0.087    0.000   11.281    0.001 /path/to/my/project/common/integrity/models/cache.py:1068(get)
     9990    0.040    0.000    8.161    0.001 /usr/local/lib/python2.7/dist-packages/django/db/models/query.py:547(filter)
     9990    0.110    0.000    8.121    0.001 /path/to/my/project/common/integrity/models/cache.py:1047(_filter_or_exclude)
     9990    0.127    0.000    7.983    0.001 /usr/local/lib/python2.7/dist-packages/django/db/models/query.py:561(_filter_or_exclude)
     9990    0.100    0.000    5.593    0.001 /path/to/my/project/common/integrity/models/cache.py:765(_clone)
     9990    0.122    0.000    5.125    0.001 /usr/local/lib/python2.7/dist-packages/django/db/models/query.py:772(_clone)
     9990    0.405    0.000    4.899    0.000 /usr/local/lib/python2.7/dist-packages/django/db/models/sql/query.py:226(clone)
129942/49972 1.456    0.000    4.505    0.000 /usr/lib/python2.7/copy.py:145(deepcopy)
129899/99929 0.191    0.000    3.117    0.000 {len}
     9990    0.111    0.000    2.968    0.000 /usr/local/lib/python2.7/dist-packages/django/db/models/query.py:74(__len__)
    19980    0.070    0.000    2.843    0.000 /path/to/my/project/common/integrity/models/cache.py:1062(iterator)
     9990    0.208    0.000    2.190    0.000 /path/to/my/project/common/integrity/models/cache.py:973(_query)
     9990    0.182    0.000    2.114    0.000 /usr/local/lib/python2.7/dist-packages/django/db/models/sql/query.py:1149(add_q)
19984/9994   0.291    0.000    1.644    0.000 /usr/lib/python2.7/copy.py:234(_deepcopy_tuple)
     9990    0.288    0.000    1.599    0.000 /usr/local/lib/python2.7/dist-packages/django/db/models/sql/query.py:997(add_filter)
     9990    0.171    0.000    1.454    0.000 /path/to/my/project/common/integrity/models/cache.py:892(_deduct)
    19980    0.177    0.000    1.208    0.000 /usr/local/lib/python2.7/dist-packages/django/utils/tree.py:55(__deepcopy__)
     9990    0.099    0.000    1.199    0.000 /path/to/my/project/common/integrity/models/cache.py:836(_deduct_recur)
     9990    0.349    0.000    1.040    0.000 /path/to/my/project/common/integrity/models/cache.py:789(_deduct_local)

抛开PyPy可能对您的案例而言本质上较慢的事实，有一些因素可能使其不必要地变慢：

已知轮廓分析可以使PyPy比CPython慢得多。

一些调试/日志记录代码可以禁用优化（例如，通过强制帧）。

您使用的服务器可能是性能的主要因素（想想经典CGI会如何与JIT一起使用：它永远不会变暖）。它也可以简单地影响结果（不同的WSGI服务器显示出不同的加速）。

旧式课程比新式课程慢。

即使一切都在内存中，你可能会在PyPy的SQLite中遇到例如慢路径。

您也可以查看JIT Friendliness wiki页面，了解有关可以使PyPy变慢的更多提示。每晚构建也可能会更快，因为相对于1.5有很多改进。

关于你的栈（服务器，操作系统，数据库）和设置（你是如何进行基准测试？有多少查询？）的更详细的描述将允许我们给出更好的答案。

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