Mercurial > hg
view tests/test-hgk.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 | 5fb1fc2e1281 |
children |
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Minimal hgk check $ echo "[extensions]" >> $HGRCPATH $ echo "hgk=" >> $HGRCPATH $ hg init repo $ cd repo $ echo a > a $ hg ci -Am adda adding a $ hg debug-cat-file commit 0 tree a0c8bcbbb45c parent 000000000000 author test 0 0 revision 0 branch default phase draft adda $ echo b > b $ hg ci -Am addb adding b $ hg log -T '{node}\n' 102a90ea7b4a3361e4082ed620918c261189a36a 07f4944404050f47db2e5c5071e0e84e7a27bba9 $ hg debug-diff-tree 07f494440405 102a90ea7b4a :000000 100664 000000000000 1e88685f5dde N b b $ hg debug-diff-tree 07f494440405 102a90ea7b4a --patch diff --git a/b b/b new file mode 100644 --- /dev/null +++ b/b @@ -0,0 +1,1 @@ +b Ensure that diff-tree output isn't affected by diffopts $ hg --config diff.noprefix=True debug-diff-tree 07f494440405 102a90ea7b4a :000000 100664 000000000000 1e88685f5dde N b b $ hg --config diff.noprefix=True debug-diff-tree --patch 07f494440405 102a90ea7b4a diff --git a/b b/b new file mode 100644 --- /dev/null +++ b/b @@ -0,0 +1,1 @@ +b $ cd ..