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view tests/test-mq-pull-from-bundle.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 | 45a4799174a1 |
children | 89630d0b3e23 |
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#require repobundlerepo $ cat <<EOF >> $HGRCPATH > [extensions] > mq= > [alias] > tlog = log --template "{rev}: {node|short} {desc}\\n" > theads = heads --template "{rev}: {desc}\\n" > tincoming = incoming --template "{rev}: {desc}\\n" > EOF Setup main: $ hg init base $ cd base $ echo "One" > one $ hg add adding one $ hg ci -m "main: one added" $ echo "++" >> one $ hg ci -m "main: one updated" Bundle main: $ hg bundle --base=null ../main.hg 2 changesets found $ cd .. Incoming to fresh repo: $ hg init fresh $ hg -R fresh tincoming main.hg comparing with main.hg 0: main: one added 1: main: one updated $ test -f ./fresh/.hg/hg-bundle* && echo 'temp. bundle file remained' || true $ hg -R fresh tincoming bundle:fresh+main.hg comparing with bundle:fresh+main.hg 0: main: one added 1: main: one updated Setup queue: $ cd base $ hg qinit -c $ hg qnew -m "patch: two added" two.patch $ echo two > two $ hg add adding two $ hg qrefresh $ hg qcommit -m "queue: two.patch added" $ hg qpop -a popping two.patch patch queue now empty Bundle queue: $ hg -R .hg/patches bundle --base=null ../queue.hgq 1 changesets found $ test -f ./fresh/.hg/hg-bundle* && echo 'temp. bundle file remained' || true $ cd .. Clone base: $ hg clone base copy updating to branch default 1 files updated, 0 files merged, 0 files removed, 0 files unresolved $ cd copy $ hg qinit -c Incoming queue bundle: $ hg -R .hg/patches tincoming ../queue.hgq comparing with ../queue.hgq 0: queue: two.patch added $ test -f .hg/hg-bundle* && echo 'temp. bundle file remained' || true Pull queue bundle: $ hg -R .hg/patches pull --update ../queue.hgq pulling from ../queue.hgq requesting all changes adding changesets adding manifests adding file changes added 1 changesets with 3 changes to 3 files new changesets d7553909353d merging series 2 files updated, 1 files merged, 0 files removed, 0 files unresolved $ test -f .hg/patches/hg-bundle* && echo 'temp. bundle file remained' || true $ hg -R .hg/patches theads 0: queue: two.patch added $ hg -R .hg/patches tlog 0: d7553909353d queue: two.patch added $ hg qseries two.patch $ cd .. Clone base again: $ hg clone base copy2 updating to branch default 1 files updated, 0 files merged, 0 files removed, 0 files unresolved $ cd copy2 $ hg qinit -c Unbundle queue bundle: $ hg -R .hg/patches unbundle --update ../queue.hgq adding changesets adding manifests adding file changes added 1 changesets with 3 changes to 3 files new changesets d7553909353d merging series 2 files updated, 1 files merged, 0 files removed, 0 files unresolved $ hg -R .hg/patches theads 0: queue: two.patch added $ hg -R .hg/patches tlog 0: d7553909353d queue: two.patch added $ hg qseries two.patch $ cd ..