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view hgdemandimport/__init__.py @ 38732:be4984261611
merge: mark file gets as not thread safe (issue5933)
In default installs, this has the effect of disabling the thread-based
worker on Windows when manifesting files in the working directory. My
measurements have shown that with revlog-based repositories, Mercurial
spends a lot of CPU time in revlog code resolving file data. This ends
up incurring a lot of context switching across threads and slows down
`hg update` operations when going from an empty working directory to
the tip of the repo.
On mozilla-unified (246,351 files) on an i7-6700K (4+4 CPUs):
before: 487s wall
after: 360s wall (equivalent to worker.enabled=false)
cpus=2: 379s wall
Even with only 2 threads, the thread pool is still slower.
The introduction of the thread-based worker (02b36e860e0b) states that
it resulted in a "~50%" speedup for `hg sparse --enable-profile` and
`hg sparse --disable-profile`. This disagrees with my measurement
above. I theorize a few reasons for this:
1) Removal of files from the working directory is I/O - not CPU - bound
and should benefit from a thread pool (unless I/O is insanely fast
and the GIL release is near instantaneous). So tests like `hg sparse
--enable-profile` may exercise deletion throughput and aren't good
benchmarks for worker tasks that are CPU heavy.
2) The patch was authored by someone at Facebook. The results were
likely measured against a repository using remotefilelog. And I
believe that revision retrieval during working directory updates with
remotefilelog will often use a remote store, thus being I/O and not
CPU bound. This probably resulted in an overstated performance gain.
Since there appears to be a need to enable the thread-based worker with
some stores, I've made the flagging of file gets as thread safe
configurable. I've made it experimental because I don't want to formalize
a boolean flag for this option and because this attribute is best
captured against the store implementation. But we don't have a proper
store API for this yet. I'd rather cross this bridge later.
It is possible there are revlog-based repositories that do benefit from
a thread-based worker. I didn't do very comprehensive testing. If there
are, we may want to devise a more proper algorithm for whether to use
the thread-based worker, including possibly config options to limit the
number of threads to use. But until I see evidence that justifies
complexity, simplicity wins.
Differential Revision: https://phab.mercurial-scm.org/D3963
author | Gregory Szorc <gregory.szorc@gmail.com> |
---|---|
date | Wed, 18 Jul 2018 09:49:34 -0700 |
parents | 670eb4fa1b86 |
children | 2372284d9457 |
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# hgdemandimport - global demand-loading of modules for Mercurial # # Copyright 2017 Facebook Inc. # # This software may be used and distributed according to the terms of the # GNU General Public License version 2 or any later version. '''demandimport - automatic demand-loading of modules''' # This is in a separate package from mercurial because in Python 3, # demand loading is per-package. Keeping demandimport in the mercurial package # would disable demand loading for any modules in mercurial. from __future__ import absolute_import import os import sys if sys.version_info[0] >= 3: from . import demandimportpy3 as demandimport else: from . import demandimportpy2 as demandimport # Full module names which can't be lazy imported. # Extensions can add to this set. IGNORES = { '__future__', '_hashlib', # ImportError during pkg_resources/__init__.py:fixup_namespace_package '_imp', '_xmlplus', 'fcntl', 'nt', # pathlib2 tests the existence of built-in 'nt' module 'win32com.gen_py', 'win32com.shell', # 'appdirs' tries to import win32com.shell '_winreg', # 2.7 mimetypes needs immediate ImportError 'pythoncom', # imported by tarfile, not available under Windows 'pwd', 'grp', # imported by profile, itself imported by hotshot.stats, # not available under Windows 'resource', # this trips up many extension authors 'gtk', # setuptools' pkg_resources.py expects "from __main__ import x" to # raise ImportError if x not defined '__main__', '_ssl', # conditional imports in the stdlib, issue1964 '_sre', # issue4920 'rfc822', 'mimetools', 'sqlalchemy.events', # has import-time side effects (issue5085) # setuptools 8 expects this module to explode early when not on windows 'distutils.msvc9compiler', '__builtin__', 'builtins', 'urwid.command_map', # for pudb } _pypy = '__pypy__' in sys.builtin_module_names if _pypy: # _ctypes.pointer is shadowed by "from ... import pointer" (PyPy 5) IGNORES.add('_ctypes.pointer') demandimport.init(IGNORES) # Re-export. isenabled = demandimport.isenabled disable = demandimport.disable deactivated = demandimport.deactivated def enable(): # chg pre-imports modules so do not enable demandimport for it if ('CHGINTERNALMARK' not in os.environ and os.environ.get('HGDEMANDIMPORT') != 'disable'): demandimport.enable()