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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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debugshell.py
59 lines | 1.4 KiB | text/x-python | PythonLexer
# debugshell extension
"""a python shell with repo, changelog & manifest objects"""
from __future__ import absolute_import
import code
import mercurial
import sys
from mercurial import (
demandimport,
registrar,
)
cmdtable = {}
command = registrar.command(cmdtable)
def pdb(ui, repo, msg, **opts):
objects = {
'mercurial': mercurial,
'repo': repo,
'cl': repo.changelog,
'mf': repo.manifestlog,
}
code.interact(msg, local=objects)
def ipdb(ui, repo, msg, **opts):
import IPython
cl = repo.changelog
mf = repo.manifestlog
cl, mf # use variables to appease pyflakes
IPython.embed()
@command('debugshell|dbsh', [])
def debugshell(ui, repo, **opts):
bannermsg = "loaded repo : %s\n" \
"using source: %s" % (repo.root,
mercurial.__path__[0])
pdbmap = {
'pdb' : 'code',
'ipdb' : 'IPython'
}
debugger = ui.config("ui", "debugger")
if not debugger:
debugger = 'pdb'
# if IPython doesn't exist, fallback to code.interact
try:
with demandimport.deactivated():
__import__(pdbmap[debugger])
except ImportError:
ui.warn(("%s debugger specified but %s module was not found\n")
% (debugger, pdbmap[debugger]))
debugger = 'pdb'
getattr(sys.modules[__name__], debugger)(ui, repo, bannermsg, **opts)