Mercurial > hg
view tests/test-custom-filters.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 | 6e713711331b |
children | ee9981bc8b44 |
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$ hg init $ cat > .hg/hgrc <<EOF > [extensions] > prefixfilter = prefix.py > [encode] > *.txt = stripprefix: Copyright 2046, The Masters > [decode] > *.txt = insertprefix: Copyright 2046, The Masters > EOF $ cat > prefix.py <<EOF > from mercurial import error > def stripprefix(s, cmd, filename, **kwargs): > header = b'%s\n' % cmd > if s[:len(header)] != header: > raise error.Abort(b'missing header "%s" in %s' % (cmd, filename)) > return s[len(header):] > def insertprefix(s, cmd): > return b'%s\n%s' % (cmd, s) > def reposetup(ui, repo): > repo.adddatafilter(b'stripprefix:', stripprefix) > repo.adddatafilter(b'insertprefix:', insertprefix) > EOF $ cat > .hgignore <<EOF > .hgignore > prefix.py > prefix.pyc > EOF $ cat > stuff.txt <<EOF > Copyright 2046, The Masters > Some stuff to ponder very carefully. > EOF $ hg add stuff.txt $ hg ci -m stuff Repository data: $ hg cat stuff.txt Some stuff to ponder very carefully. Fresh checkout: $ rm stuff.txt $ hg up -C 1 files updated, 0 files merged, 0 files removed, 0 files unresolved $ cat stuff.txt Copyright 2046, The Masters Some stuff to ponder very carefully. $ echo "Very very carefully." >> stuff.txt $ hg stat M stuff.txt $ echo "Unauthorized material subject to destruction." > morestuff.txt Problem encoding: $ hg add morestuff.txt $ hg ci -m morestuff abort: missing header "Copyright 2046, The Masters" in morestuff.txt [255] $ hg stat M stuff.txt A morestuff.txt