Mercurial > hg
view tests/fakedirstatewritetime.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 | c6061cadb400 |
children | fdd4d668ceb5 |
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# extension to emulate invoking 'dirstate.write()' at the time # specified by '[fakedirstatewritetime] fakenow', only when # 'dirstate.write()' is invoked via functions below: # # - 'workingctx._poststatusfixup()' (= 'repo.status()') # - 'committablectx.markcommitted()' from __future__ import absolute_import from mercurial import ( context, dirstate, extensions, policy, registrar, ) from mercurial.utils import dateutil configtable = {} configitem = registrar.configitem(configtable) configitem(b'fakedirstatewritetime', b'fakenow', default=None, ) parsers = policy.importmod(r'parsers') def pack_dirstate(fakenow, orig, dmap, copymap, pl, now): # execute what original parsers.pack_dirstate should do actually # for consistency actualnow = int(now) for f, e in dmap.items(): if e[0] == 'n' and e[3] == actualnow: e = parsers.dirstatetuple(e[0], e[1], e[2], -1) dmap[f] = e return orig(dmap, copymap, pl, fakenow) def fakewrite(ui, func): # fake "now" of 'pack_dirstate' only if it is invoked while 'func' fakenow = ui.config(b'fakedirstatewritetime', b'fakenow') if not fakenow: # Execute original one, if fakenow isn't configured. This is # useful to prevent subrepos from executing replaced one, # because replacing 'parsers.pack_dirstate' is also effective # in subrepos. return func() # parsing 'fakenow' in YYYYmmddHHMM format makes comparison between # 'fakenow' value and 'touch -t YYYYmmddHHMM' argument easy fakenow = dateutil.parsedate(fakenow, [b'%Y%m%d%H%M'])[0] orig_pack_dirstate = parsers.pack_dirstate orig_dirstate_getfsnow = dirstate._getfsnow wrapper = lambda *args: pack_dirstate(fakenow, orig_pack_dirstate, *args) parsers.pack_dirstate = wrapper dirstate._getfsnow = lambda *args: fakenow try: return func() finally: parsers.pack_dirstate = orig_pack_dirstate dirstate._getfsnow = orig_dirstate_getfsnow def _poststatusfixup(orig, workingctx, status, fixup): ui = workingctx.repo().ui return fakewrite(ui, lambda : orig(workingctx, status, fixup)) def markcommitted(orig, committablectx, node): ui = committablectx.repo().ui return fakewrite(ui, lambda : orig(committablectx, node)) def extsetup(ui): extensions.wrapfunction(context.workingctx, '_poststatusfixup', _poststatusfixup) extensions.wrapfunction(context.committablectx, 'markcommitted', markcommitted)