Mercurial > hg
view tests/test-requires.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 | ecac0006b90e |
children | fed5e57c8dc7 |
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$ hg init t $ cd t $ echo a > a $ hg add a $ hg commit -m test $ rm .hg/requires $ hg tip abort: unknown version (2) in revlog 00changelog.i! [255] $ echo indoor-pool > .hg/requires $ hg tip abort: repository requires features unknown to this Mercurial: indoor-pool! (see https://mercurial-scm.org/wiki/MissingRequirement for more information) [255] $ echo outdoor-pool >> .hg/requires $ hg tip abort: repository requires features unknown to this Mercurial: indoor-pool outdoor-pool! (see https://mercurial-scm.org/wiki/MissingRequirement for more information) [255] $ cd .. Test checking between features supported locally and ones required in another repository of push/pull/clone on localhost: $ mkdir supported-locally $ cd supported-locally $ hg init supported $ echo a > supported/a $ hg -R supported commit -Am '#0 at supported' adding a $ echo 'featuresetup-test' >> supported/.hg/requires $ cat > $TESTTMP/supported-locally/supportlocally.py <<EOF > from __future__ import absolute_import > from mercurial import extensions, localrepo > def featuresetup(ui, supported): > for name, module in extensions.extensions(ui): > if __name__ == module.__name__: > # support specific feature locally > supported |= {'featuresetup-test'} > return > def uisetup(ui): > localrepo.featuresetupfuncs.add(featuresetup) > EOF $ cat > supported/.hg/hgrc <<EOF > [extensions] > # enable extension locally > supportlocally = $TESTTMP/supported-locally/supportlocally.py > EOF $ hg -R supported status $ hg init push-dst $ hg -R supported push push-dst pushing to push-dst abort: required features are not supported in the destination: featuresetup-test [255] $ hg init pull-src $ hg -R pull-src pull supported pulling from supported abort: required features are not supported in the destination: featuresetup-test [255] $ hg clone supported clone-dst abort: repository requires features unknown to this Mercurial: featuresetup-test! (see https://mercurial-scm.org/wiki/MissingRequirement for more information) [255] $ hg clone --pull supported clone-dst abort: required features are not supported in the destination: featuresetup-test [255] $ cd ..