Mercurial > hg
view tests/test-parents.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 | 4441705b7111 |
children | 8d72e29ad1e0 |
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test parents command $ hg init repo $ cd repo no working directory $ hg parents $ echo a > a $ echo b > b $ hg ci -Amab -d '0 0' adding a adding b $ echo a >> a $ hg ci -Ama -d '1 0' $ echo b >> b $ hg ci -Amb -d '2 0' $ echo c > c $ hg ci -Amc -d '3 0' adding c $ hg up -C 1 1 files updated, 0 files merged, 1 files removed, 0 files unresolved $ echo d > c $ hg ci -Amc2 -d '4 0' adding c created new head $ hg up -C 3 2 files updated, 0 files merged, 0 files removed, 0 files unresolved $ hg parents changeset: 3:02d851b7e549 user: test date: Thu Jan 01 00:00:03 1970 +0000 summary: c $ hg parents a changeset: 1:d786049f033a user: test date: Thu Jan 01 00:00:01 1970 +0000 summary: a hg parents c, single revision $ hg parents c changeset: 3:02d851b7e549 user: test date: Thu Jan 01 00:00:03 1970 +0000 summary: c $ hg parents -r 3 c abort: 'c' not found in manifest! [255] $ hg parents -r 2 changeset: 1:d786049f033a user: test date: Thu Jan 01 00:00:01 1970 +0000 summary: a $ hg parents -r 2 a changeset: 1:d786049f033a user: test date: Thu Jan 01 00:00:01 1970 +0000 summary: a $ hg parents -r 2 ../a abort: ../a not under root '$TESTTMP/repo' [255] cd dir; hg parents -r 2 ../a $ mkdir dir $ cd dir $ hg parents -r 2 ../a changeset: 1:d786049f033a user: test date: Thu Jan 01 00:00:01 1970 +0000 summary: a $ hg parents -r 2 path:a changeset: 1:d786049f033a user: test date: Thu Jan 01 00:00:01 1970 +0000 summary: a $ cd .. $ hg parents -r 2 glob:a abort: can only specify an explicit filename [255] merge working dir with 2 parents, hg parents c $ HGMERGE=true hg merge merging c 0 files updated, 1 files merged, 0 files removed, 0 files unresolved (branch merge, don't forget to commit) $ hg parents c changeset: 3:02d851b7e549 user: test date: Thu Jan 01 00:00:03 1970 +0000 summary: c changeset: 4:48cee28d4b4e tag: tip parent: 1:d786049f033a user: test date: Thu Jan 01 00:00:04 1970 +0000 summary: c2 merge working dir with 1 parent, hg parents $ hg up -C 2 0 files updated, 0 files merged, 1 files removed, 0 files unresolved $ HGMERGE=true hg merge -r 4 1 files updated, 0 files merged, 0 files removed, 0 files unresolved (branch merge, don't forget to commit) $ hg parents changeset: 2:6cfac479f009 user: test date: Thu Jan 01 00:00:02 1970 +0000 summary: b changeset: 4:48cee28d4b4e tag: tip parent: 1:d786049f033a user: test date: Thu Jan 01 00:00:04 1970 +0000 summary: c2 merge working dir with 1 parent, hg parents c $ hg parents c changeset: 4:48cee28d4b4e tag: tip parent: 1:d786049f033a user: test date: Thu Jan 01 00:00:04 1970 +0000 summary: c2 $ cd ..