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merge: mark file gets as not thread safe (issue5933)...
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

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dirstatenonnormalcheck.py
59 lines | 2.6 KiB | text/x-python | PythonLexer
/ contrib / dirstatenonnormalcheck.py
# dirstatenonnormalcheck.py - extension to check the consistency of the
# dirstate's non-normal map
#
# For most operations on dirstate, this extensions checks that the nonnormalset
# contains the right entries.
# It compares the nonnormal file to a nonnormalset built from the map of all
# the files in the dirstate to check that they contain the same files.
from __future__ import absolute_import
from mercurial import (
dirstate,
extensions,
)
def nonnormalentries(dmap):
"""Compute nonnormal entries from dirstate's dmap"""
res = set()
for f, e in dmap.iteritems():
if e[0] != b'n' or e[3] == -1:
res.add(f)
return res
def checkconsistency(ui, orig, dmap, _nonnormalset, label):
"""Compute nonnormalset from dmap, check that it matches _nonnormalset"""
nonnormalcomputedmap = nonnormalentries(dmap)
if _nonnormalset != nonnormalcomputedmap:
ui.develwarn(b"%s call to %s\n" % (label, orig), config=b'dirstate')
ui.develwarn(b"inconsistency in nonnormalset\n", config=b'dirstate')
ui.develwarn(b"[nonnormalset] %s\n" % _nonnormalset, config=b'dirstate')
ui.develwarn(b"[map] %s\n" % nonnormalcomputedmap, config=b'dirstate')
def _checkdirstate(orig, self, arg):
"""Check nonnormal set consistency before and after the call to orig"""
checkconsistency(self._ui, orig, self._map, self._map.nonnormalset,
b"before")
r = orig(self, arg)
checkconsistency(self._ui, orig, self._map, self._map.nonnormalset,
b"after")
return r
def extsetup(ui):
"""Wrap functions modifying dirstate to check nonnormalset consistency"""
dirstatecl = dirstate.dirstate
devel = ui.configbool(b'devel', b'all-warnings')
paranoid = ui.configbool(b'experimental', b'nonnormalparanoidcheck')
if devel:
extensions.wrapfunction(dirstatecl, '_writedirstate', _checkdirstate)
if paranoid:
# We don't do all these checks when paranoid is disable as it would
# make the extension run very slowly on large repos
extensions.wrapfunction(dirstatecl, 'normallookup', _checkdirstate)
extensions.wrapfunction(dirstatecl, 'otherparent', _checkdirstate)
extensions.wrapfunction(dirstatecl, 'normal', _checkdirstate)
extensions.wrapfunction(dirstatecl, 'write', _checkdirstate)
extensions.wrapfunction(dirstatecl, 'add', _checkdirstate)
extensions.wrapfunction(dirstatecl, 'remove', _checkdirstate)
extensions.wrapfunction(dirstatecl, 'merge', _checkdirstate)
extensions.wrapfunction(dirstatecl, 'drop', _checkdirstate)