Mercurial > hg
view tests/test-walkrepo.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 | fa2423acb02f |
children | 2372284d9457 |
line wrap: on
line source
from __future__ import absolute_import, print_function import os from mercurial import ( hg, scmutil, ui as uimod, util, ) chdir = os.chdir mkdir = os.mkdir pjoin = os.path.join walkrepos = scmutil.walkrepos checklink = util.checklink u = uimod.ui.load() sym = checklink(b'.') hg.repository(u, b'top1', create=1) mkdir(b'subdir') chdir(b'subdir') hg.repository(u, b'sub1', create=1) mkdir(b'subsubdir') chdir(b'subsubdir') hg.repository(u, b'subsub1', create=1) chdir(os.path.pardir) if sym: os.symlink(os.path.pardir, b'circle') os.symlink(pjoin(b'subsubdir', b'subsub1'), b'subsub1') def runtest(): reposet = frozenset(walkrepos(b'.', followsym=True)) if sym and (len(reposet) != 3): print("reposet = %r" % (reposet,)) print(("Found %d repositories when I should have found 3" % (len(reposet),))) if (not sym) and (len(reposet) != 2): print("reposet = %r" % (reposet,)) print(("Found %d repositories when I should have found 2" % (len(reposet),))) sub1set = frozenset((pjoin(b'.', b'sub1'), pjoin(b'.', b'circle', b'subdir', b'sub1'))) if len(sub1set & reposet) != 1: print("sub1set = %r" % (sub1set,)) print("reposet = %r" % (reposet,)) print("sub1set and reposet should have exactly one path in common.") sub2set = frozenset((pjoin(b'.', b'subsub1'), pjoin(b'.', b'subsubdir', b'subsub1'))) if len(sub2set & reposet) != 1: print("sub2set = %r" % (sub2set,)) print("reposet = %r" % (reposet,)) print("sub2set and reposet should have exactly one path in common.") sub3 = pjoin(b'.', b'circle', b'top1') if sym and sub3 not in reposet: print("reposet = %r" % (reposet,)) print("Symbolic links are supported and %s is not in reposet" % (sub3,)) runtest() if sym: # Simulate not having symlinks. del os.path.samestat sym = False runtest()