Mercurial > hg
view tests/test-demandimport.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 | 1d0610fdd63b |
children | dffd6a301570 |
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from __future__ import absolute_import, print_function from mercurial import demandimport demandimport.enable() import os import subprocess import sys # Only run if demandimport is allowed if subprocess.call(['python', '%s/hghave' % os.environ['TESTDIR'], 'demandimport']): sys.exit(80) if os.name != 'nt': try: import distutils.msvc9compiler print('distutils.msvc9compiler needs to be an immediate ' 'importerror on non-windows platforms') distutils.msvc9compiler except ImportError: pass import re rsub = re.sub def f(obj): l = repr(obj) l = rsub("0x[0-9a-fA-F]+", "0x?", l) l = rsub("from '.*'", "from '?'", l) l = rsub("'<[a-z]*>'", "'<whatever>'", l) return l demandimport.disable() os.environ['HGDEMANDIMPORT'] = 'disable' # this enable call should not actually enable demandimport! demandimport.enable() from mercurial import node print("node =", f(node)) # now enable it for real del os.environ['HGDEMANDIMPORT'] demandimport.enable() # Test access to special attributes through demandmod proxy from mercurial import error as errorproxy print("errorproxy =", f(errorproxy)) print("errorproxy.__doc__ = %r" % (' '.join(errorproxy.__doc__.split()[:3]) + ' ...')) print("errorproxy.__name__ = %r" % errorproxy.__name__) # __name__ must be accessible via __dict__ so the relative imports can be # resolved print("errorproxy.__dict__['__name__'] = %r" % errorproxy.__dict__['__name__']) print("errorproxy =", f(errorproxy)) import os print("os =", f(os)) print("os.system =", f(os.system)) print("os =", f(os)) from mercurial.utils import procutil print("procutil =", f(procutil)) print("procutil.system =", f(procutil.system)) print("procutil =", f(procutil)) print("procutil.system =", f(procutil.system)) from mercurial import hgweb print("hgweb =", f(hgweb)) print("hgweb_mod =", f(hgweb.hgweb_mod)) print("hgweb =", f(hgweb)) import re as fred print("fred =", f(fred)) import re as remod print("remod =", f(remod)) import sys as re print("re =", f(re)) print("fred =", f(fred)) print("fred.sub =", f(fred.sub)) print("fred =", f(fred)) remod.escape # use remod print("remod =", f(remod)) print("re =", f(re)) print("re.stderr =", f(re.stderr)) print("re =", f(re)) import contextlib print("contextlib =", f(contextlib)) try: from contextlib import unknownattr print('no demandmod should be created for attribute of non-package ' 'module:\ncontextlib.unknownattr =', f(unknownattr)) except ImportError as inst: print('contextlib.unknownattr = ImportError: %s' % rsub(r"'", '', str(inst))) from mercurial import util # Unlike the import statement, __import__() function should not raise # ImportError even if fromlist has an unknown item # (see Python/import.c:import_module_level() and ensure_fromlist()) contextlibimp = __import__('contextlib', globals(), locals(), ['unknownattr']) print("__import__('contextlib', ..., ['unknownattr']) =", f(contextlibimp)) print("hasattr(contextlibimp, 'unknownattr') =", util.safehasattr(contextlibimp, 'unknownattr'))