Mercurial > hg
view tests/test-check-help.t @ 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 | 80e5210df25c |
children | d2c81e83de2a |
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#require test-repo $ . "$TESTDIR/helpers-testrepo.sh" $ cat <<'EOF' > scanhelptopics.py > from __future__ import absolute_import, print_function > import re > import sys > if sys.platform == "win32": > import os, msvcrt > msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY) > topics = set() > topicre = re.compile(br':hg:`help ([a-z0-9\-.]+)`') > for fname in sys.argv: > with open(fname, 'rb') as f: > topics.update(m.group(1) for m in topicre.finditer(f.read())) > for s in sorted(topics): > print(s) > EOF $ cd "$TESTDIR"/.. Check if ":hg:`help TOPIC`" is valid: (use "xargs -n1 -t" to see which help commands are executed) $ testrepohg files 'glob:{hgdemandimport,hgext,mercurial}/**/*.py' \ > | sed 's|\\|/|g' \ > | xargs $PYTHON "$TESTTMP/scanhelptopics.py" \ > | xargs -n1 hg help > /dev/null