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view mercurial/pushkey.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> |
---|---|
date | Wed, 18 Jul 2018 09:49:34 -0700 |
parents | 7b200566e474 |
children | 57875cf423c9 |
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# pushkey.py - dispatching for pushing and pulling keys # # Copyright 2010 Matt Mackall <mpm@selenic.com> # # This software may be used and distributed according to the terms of the # GNU General Public License version 2 or any later version. from __future__ import absolute_import from . import ( bookmarks, encoding, obsolete, phases, ) def _nslist(repo): n = {} for k in _namespaces: n[k] = "" if not obsolete.isenabled(repo, obsolete.exchangeopt): n.pop('obsolete') return n _namespaces = {"namespaces": (lambda *x: False, _nslist), "bookmarks": (bookmarks.pushbookmark, bookmarks.listbookmarks), "phases": (phases.pushphase, phases.listphases), "obsolete": (obsolete.pushmarker, obsolete.listmarkers), } def register(namespace, pushkey, listkeys): _namespaces[namespace] = (pushkey, listkeys) def _get(namespace): return _namespaces.get(namespace, (lambda *x: False, lambda *x: {})) def push(repo, namespace, key, old, new): '''should succeed iff value was old''' pk = _get(namespace)[0] return pk(repo, key, old, new) def list(repo, namespace): '''return a dict''' lk = _get(namespace)[1] return lk(repo) encode = encoding.fromlocal decode = encoding.tolocal def encodekeys(keys): """encode the content of a pushkey namespace for exchange over the wire""" return '\n'.join(['%s\t%s' % (encode(k), encode(v)) for k, v in keys]) def decodekeys(data): """decode the content of a pushkey namespace from exchange over the wire""" result = {} for l in data.splitlines(): k, v = l.split('\t') result[decode(k)] = decode(v) return result