Mercurial > hg
view tests/test-merge10.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 | eb586ed5d8ce |
children | faa49a5914bb |
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Test for changeset 9fe267f77f56ff127cf7e65dc15dd9de71ce8ceb (merge correctly when all the files in a directory are moved but then local changes are added in the same directory) $ hg init a $ cd a $ mkdir -p testdir $ echo a > testdir/a $ hg add testdir/a $ hg commit -m a $ cd .. $ hg clone a b updating to branch default 1 files updated, 0 files merged, 0 files removed, 0 files unresolved $ cd a $ echo alpha > testdir/a $ hg commit -m remote-change $ cd .. $ cd b $ mkdir testdir/subdir $ hg mv testdir/a testdir/subdir/a $ hg commit -m move $ mkdir newdir $ echo beta > newdir/beta $ hg add newdir/beta $ hg commit -m local-addition $ hg pull ../a pulling from ../a searching for changes adding changesets adding manifests adding file changes added 1 changesets with 1 changes to 1 files (+1 heads) new changesets cc7000b01af9 (run 'hg heads' to see heads, 'hg merge' to merge) $ hg up -C 2 0 files updated, 0 files merged, 0 files removed, 0 files unresolved $ hg merge merging testdir/subdir/a and testdir/a to testdir/subdir/a 0 files updated, 1 files merged, 0 files removed, 0 files unresolved (branch merge, don't forget to commit) $ hg stat M testdir/subdir/a $ hg diff --nodates diff -r bc21c9773bfa testdir/subdir/a --- a/testdir/subdir/a +++ b/testdir/subdir/a @@ -1,1 +1,1 @@ -a +alpha $ cd ..