Mercurial > hg
view tests/test-narrow-merge.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 | dc01484606da |
children | 8e855e9984a6 |
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#testcases flat tree $ . "$TESTDIR/narrow-library.sh" #if tree $ cat << EOF >> $HGRCPATH > [experimental] > treemanifest = 1 > EOF #endif create full repo $ hg init master $ cd master $ cat >> .hg/hgrc <<EOF > [narrow] > serveellipses=True > EOF $ mkdir inside $ echo inside1 > inside/f1 $ echo inside2 > inside/f2 $ mkdir outside $ echo outside1 > outside/f1 $ echo outside2 > outside/f2 $ hg ci -Aqm 'initial' $ echo modified > inside/f1 $ hg ci -qm 'modify inside/f1' $ hg update -q 0 $ echo modified > inside/f2 $ hg ci -qm 'modify inside/f2' $ hg update -q 0 $ echo modified2 > inside/f1 $ hg ci -qm 'conflicting inside/f1' $ hg update -q 0 $ echo modified > outside/f1 $ hg ci -qm 'modify outside/f1' $ hg update -q 0 $ echo modified2 > outside/f1 $ hg ci -qm 'conflicting outside/f1' $ cd .. $ hg clone --narrow ssh://user@dummy/master narrow --include inside requesting all changes adding changesets adding manifests adding file changes added 6 changesets with 5 changes to 2 files (+4 heads) new changesets *:* (glob) updating to branch default 2 files updated, 0 files merged, 0 files removed, 0 files unresolved $ cd narrow $ hg update -q 0 Can merge in when no files outside narrow spec are involved $ hg update -q 'desc("modify inside/f1")' $ hg merge 'desc("modify inside/f2")' 1 files updated, 0 files merged, 0 files removed, 0 files unresolved (branch merge, don't forget to commit) $ hg commit -m 'merge inside changes' Can merge conflicting changes inside narrow spec $ hg update -q 'desc("modify inside/f1")' $ hg merge 'desc("conflicting inside/f1")' 2>&1 | egrep -v '(warning:|incomplete!)' merging inside/f1 0 files updated, 0 files merged, 0 files removed, 1 files unresolved use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon $ echo modified3 > inside/f1 $ hg resolve -m (no more unresolved files) $ hg commit -m 'merge inside/f1' TODO: Can merge non-conflicting changes outside narrow spec $ hg update -q 'desc("modify inside/f1")' $ hg merge 'desc("modify outside/f1")' abort: merge affects file 'outside/f1' outside narrow, which is not yet supported (flat !) abort: merge affects file 'outside/' outside narrow, which is not yet supported (tree !) (merging in the other direction may work) [255] $ hg update -q 'desc("modify outside/f1")' $ hg merge 'desc("modify inside/f1")' 1 files updated, 0 files merged, 0 files removed, 0 files unresolved (branch merge, don't forget to commit) $ hg ci -m 'merge from inside to outside' Refuses merge of conflicting outside changes $ hg update -q 'desc("modify outside/f1")' $ hg merge 'desc("conflicting outside/f1")' abort: conflict in file 'outside/f1' is outside narrow clone (flat !) abort: conflict in file 'outside/' is outside narrow clone (tree !) [255]