Mercurial > hg
view tests/test-children.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 | 7c8524efd847 |
children |
line wrap: on
line source
test children command $ cat <<EOF >> $HGRCPATH > [extensions] > children = > EOF init $ hg init t $ cd t no working directory $ hg children setup $ echo 0 > file0 $ hg ci -qAm 0 -d '0 0' $ echo 1 > file1 $ hg ci -qAm 1 -d '1 0' $ echo 2 >> file0 $ hg ci -qAm 2 -d '2 0' $ hg co null 0 files updated, 0 files merged, 2 files removed, 0 files unresolved $ echo 3 > file3 $ hg ci -qAm 3 -d '3 0' hg children at revision 3 (tip) $ hg children $ hg co null 0 files updated, 0 files merged, 1 files removed, 0 files unresolved hg children at nullrev (should be 0 and 3) $ hg children changeset: 0:4df8521a7374 user: test date: Thu Jan 01 00:00:00 1970 +0000 summary: 0 changeset: 3:e2962852269d tag: tip parent: -1:000000000000 user: test date: Thu Jan 01 00:00:03 1970 +0000 summary: 3 $ hg co 1 2 files updated, 0 files merged, 0 files removed, 0 files unresolved hg children at revision 1 (should be 2) $ hg children changeset: 2:8f5eea5023c2 user: test date: Thu Jan 01 00:00:02 1970 +0000 summary: 2 $ hg co 2 1 files updated, 0 files merged, 0 files removed, 0 files unresolved hg children at revision 2 (other head) $ hg children $ for i in null 0 1 2 3 '2^'; do > echo "hg children -r '$i'" > hg children -r $i > done hg children -r 'null' changeset: 0:4df8521a7374 user: test date: Thu Jan 01 00:00:00 1970 +0000 summary: 0 changeset: 3:e2962852269d tag: tip parent: -1:000000000000 user: test date: Thu Jan 01 00:00:03 1970 +0000 summary: 3 hg children -r '0' changeset: 1:708c093edef0 user: test date: Thu Jan 01 00:00:01 1970 +0000 summary: 1 hg children -r '1' changeset: 2:8f5eea5023c2 user: test date: Thu Jan 01 00:00:02 1970 +0000 summary: 2 hg children -r '2' hg children -r '3' hg children -r '2^' changeset: 2:8f5eea5023c2 user: test date: Thu Jan 01 00:00:02 1970 +0000 summary: 2 hg children -r 0 file0 (should be 2) $ hg children -r 0 file0 changeset: 2:8f5eea5023c2 user: test date: Thu Jan 01 00:00:02 1970 +0000 summary: 2 hg children -r 1 file0 (should be 2) $ hg children -r 1 file0 changeset: 2:8f5eea5023c2 user: test date: Thu Jan 01 00:00:02 1970 +0000 summary: 2 $ hg co 0 1 files updated, 0 files merged, 1 files removed, 0 files unresolved hg children file0 at revision 0 (should be 2) $ hg children file0 changeset: 2:8f5eea5023c2 user: test date: Thu Jan 01 00:00:02 1970 +0000 summary: 2 should be compatible with templater (don't pass fctx to displayer) $ hg children file0 -Tdefault changeset: 2:8f5eea5023c2 user: test date: Thu Jan 01 00:00:02 1970 +0000 summary: 2 $ cd ..