Mercurial > hg
comparison mercurial/merge.py @ 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> |
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date | Wed, 18 Jul 2018 09:49:34 -0700 |
parents | d4be8ea8f22d |
children | d49e490a9e85 |
comparison
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38731:ef3838a47503 | 38732:be4984261611 |
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1635 wctx[f].audit() | 1635 wctx[f].audit() |
1636 wctx[f].write(wctx.filectx(f0).data(), wctx.filectx(f0).flags()) | 1636 wctx[f].write(wctx.filectx(f0).data(), wctx.filectx(f0).flags()) |
1637 wctx[f0].remove() | 1637 wctx[f0].remove() |
1638 progress.increment(item=f) | 1638 progress.increment(item=f) |
1639 | 1639 |
1640 # get in parallel | 1640 # get in parallel. |
1641 threadsafe = repo.ui.configbool('experimental', | |
1642 'worker.wdir-get-thread-safe') | |
1641 prog = worker.worker(repo.ui, cost, batchget, (repo, mctx, wctx), | 1643 prog = worker.worker(repo.ui, cost, batchget, (repo, mctx, wctx), |
1642 actions[ACTION_GET]) | 1644 actions[ACTION_GET], |
1645 threadsafe=threadsafe) | |
1643 for i, item in prog: | 1646 for i, item in prog: |
1644 progress.increment(step=i, item=item) | 1647 progress.increment(step=i, item=item) |
1645 updated = len(actions[ACTION_GET]) | 1648 updated = len(actions[ACTION_GET]) |
1646 | 1649 |
1647 if [a for a in actions[ACTION_GET] if a[0] == '.hgsubstate']: | 1650 if [a for a in actions[ACTION_GET] if a[0] == '.hgsubstate']: |