Mercurial > hg
view tests/test-mq-qgoto.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 | bbf544b5f2e9 |
children |
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$ echo "[extensions]" >> $HGRCPATH $ echo "mq=" >> $HGRCPATH $ hg init a $ cd a $ echo a > a $ hg ci -Ama adding a $ hg qnew a.patch $ echo a >> a $ hg qrefresh $ hg qnew b.patch $ echo b > b $ hg add b $ hg qrefresh $ hg qnew c.patch $ echo c > c $ hg add c $ hg qrefresh $ hg qgoto a.patch popping c.patch popping b.patch now at: a.patch $ hg qgoto c.patch applying b.patch applying c.patch now at: c.patch $ hg qgoto b.patch popping c.patch now at: b.patch Using index: $ hg qgoto 0 popping b.patch now at: a.patch $ hg qgoto 2 applying b.patch applying c.patch now at: c.patch No warnings when using index ... and update from non-qtip and with pending changes in unrelated files: $ hg qnew bug314159 $ echo d >> c $ hg qrefresh $ hg qnew bug141421 $ echo e >> b $ hg qrefresh $ hg up -r bug314159 1 files updated, 0 files merged, 0 files removed, 0 files unresolved $ echo f >> a $ echo f >> b $ echo f >> c $ hg qgoto 1 abort: local changes found, qrefresh first [255] $ hg qgoto 1 -f popping bug141421 popping bug314159 popping c.patch now at: b.patch $ hg st M a M b ? c.orig $ hg up -qCr. $ hg qgoto 3 applying c.patch applying bug314159 now at: bug314159 Detect ambiguous non-index: $ hg qgoto 14 patch name "14" is ambiguous: bug314159 bug141421 abort: patch 14 not in series [255] $ cd ..