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view tests/hghave @ 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> |
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date | Wed, 18 Jul 2018 09:49:34 -0700 |
parents | b1b35a9051c3 |
children | 47ef023d0165 |
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#!/usr/bin/env python """Test the running system for features availability. Exit with zero if all features are there, non-zero otherwise. If a feature name is prefixed with "no-", the absence of feature is tested. """ from __future__ import absolute_import, print_function import hghave import optparse import os import sys checks = hghave.checks def list_features(): for name, feature in sorted(checks.items()): desc = feature[1] print(name + ':', desc) def test_features(): failed = 0 for name, feature in checks.items(): check, _ = feature try: check() except Exception as e: print("feature %s failed: %s" % (name, e)) failed += 1 return failed parser = optparse.OptionParser("%prog [options] [features]") parser.add_option("--test-features", action="store_true", help="test available features") parser.add_option("--list-features", action="store_true", help="list available features") def _loadaddon(): if 'TESTDIR' in os.environ: # loading from '.' isn't needed, because `hghave` should be # running at TESTTMP in this case path = os.environ['TESTDIR'] else: path = '.' if not os.path.exists(os.path.join(path, 'hghaveaddon.py')): return sys.path.insert(0, path) try: import hghaveaddon assert hghaveaddon # silence pyflakes except BaseException as inst: sys.stderr.write('failed to import hghaveaddon.py from %r: %s\n' % (path, inst)) sys.exit(2) sys.path.pop(0) if __name__ == '__main__': options, args = parser.parse_args() _loadaddon() if options.list_features: list_features() sys.exit(0) if options.test_features: sys.exit(test_features()) hghave.require(args)