Mercurial > hg
view tests/test-merge-closedheads.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 | f2719b387380 |
children | 8197b395710e |
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$ hgcommit() { > hg commit -u user "$@" > } $ hg init clhead $ cd clhead $ touch foo && hg add && hgcommit -m 'foo' adding foo $ touch bar && hg add && hgcommit -m 'bar' adding bar $ touch baz && hg add && hgcommit -m 'baz' adding baz $ echo "flub" > foo $ hgcommit -m "flub" $ echo "nub" > foo $ hgcommit -m "nub" $ hg up -C 2 1 files updated, 0 files merged, 0 files removed, 0 files unresolved $ echo "c1" > c1 $ hg add c1 $ hgcommit -m "c1" created new head $ echo "c2" > c1 $ hgcommit -m "c2" $ hg up -C 2 0 files updated, 0 files merged, 1 files removed, 0 files unresolved $ echo "d1" > d1 $ hg add d1 $ hgcommit -m "d1" created new head $ echo "d2" > d1 $ hgcommit -m "d2" $ hg tag -l good fail with three heads $ hg up -C good 0 files updated, 0 files merged, 0 files removed, 0 files unresolved $ hg merge abort: branch 'default' has 3 heads - please merge with an explicit rev (run 'hg heads .' to see heads) [255] close one of the heads $ hg up -C 6 1 files updated, 0 files merged, 1 files removed, 0 files unresolved $ hgcommit -m 'close this head' --close-branch succeed with two open heads $ hg up -C good 1 files updated, 0 files merged, 1 files removed, 0 files unresolved $ hg up -C good 0 files updated, 0 files merged, 0 files removed, 0 files unresolved $ hg merge 1 files updated, 0 files merged, 0 files removed, 0 files unresolved (branch merge, don't forget to commit) $ hgcommit -m 'merged heads' hg update -C 8 $ hg update -C 8 1 files updated, 0 files merged, 0 files removed, 0 files unresolved hg branch some-branch $ hg branch some-branch marked working directory as branch some-branch (branches are permanent and global, did you want a bookmark?) hg commit $ hgcommit -m 'started some-branch' hg commit --close-branch $ hgcommit --close-branch -m 'closed some-branch' hg update default $ hg update default 1 files updated, 0 files merged, 0 files removed, 0 files unresolved hg merge some-branch $ hg merge some-branch 0 files updated, 0 files merged, 0 files removed, 0 files unresolved (branch merge, don't forget to commit) hg commit (no reopening of some-branch) $ hgcommit -m 'merge with closed branch' $ cd ..