Mercurial > hg
view tests/test-context-metadata.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 | 8327fd79adf8 |
children | b8db53f786f0 |
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Tests about metadataonlyctx $ hg init $ echo A > A $ hg commit -A A -m 'Add A' $ echo B > B $ hg commit -A B -m 'Add B' $ hg rm A $ echo C > C $ echo B2 > B $ hg add C -q $ hg commit -m 'Remove A' $ cat > metaedit.py <<EOF > from __future__ import absolute_import > from mercurial import context, pycompat, registrar > cmdtable = {} > command = registrar.command(cmdtable) > @command(b'metaedit') > def metaedit(ui, repo, arg): > # Modify commit message to "FOO" > with repo.wlock(), repo.lock(), repo.transaction(b'metaedit'): > old = repo[b'.'] > kwargs = dict(s.split(b'=', 1) for s in arg.split(b';')) > if 'parents' in kwargs: > kwargs[b'parents'] = map(int, kwargs[b'parents'].split(b',')) > new = context.metadataonlyctx(repo, old, > **pycompat.strkwargs(kwargs)) > new.commit() > EOF $ hg --config extensions.metaedit=$TESTTMP/metaedit.py metaedit 'text=Changed' $ hg log -r tip changeset: 3:ad83e9e00ec9 tag: tip parent: 1:3afb7afe6632 user: test date: Thu Jan 01 00:00:00 1970 +0000 summary: Changed $ hg --config extensions.metaedit=$TESTTMP/metaedit.py metaedit 'parents=0' 2>&1 | egrep '^RuntimeError' RuntimeError: can't reuse the manifest: its p1 doesn't match the new ctx p1 $ hg --config extensions.metaedit=$TESTTMP/metaedit.py metaedit 'user=foo <foo@example.com>' $ hg log -r tip changeset: 4:1f86eaeca92b tag: tip parent: 1:3afb7afe6632 user: foo <foo@example.com> date: Thu Jan 01 00:00:00 1970 +0000 summary: Remove A