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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
Gregory Szorc -
r38755:be498426 default
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Mercurial for Windows



Welcome to Mercurial for Windows!




Mercurial is a command-line application. You must run it from
the Windows command prompt (or if you're hard core, a <a<br /> href="http://www.mingw.org/">MinGW shell).




Note: the standard http://www.mingw.org/">MinGW
msys startup script uses rxvt which has problems setting up
standard input and output. Running bash directly works
correctly.




For documentation, please visit the <a<br /> href="https://mercurial-scm.org/">Mercurial web site.
You can also download a free book, <a<br /> href="https://book.mercurial-scm.org/">Mercurial: The Definitive
Guide.




By default, Mercurial installs to C:\Program
Files\Mercurial
. The Mercurial command is called
hg.exe.



Testing Mercurial after you've installed it




The easiest way to check that Mercurial is installed properly is
to just type the following at the command prompt:




hg



This command should print a useful help message. If it does,
other Mercurial commands should work fine for you.



Configuration notes


Default editor



The default editor for commit messages is 'notepad'. You can set
the EDITOR (or HGEDITOR) environment variable
to specify your preference or set it in mercurial.ini:



[ui]
editor = whatever


Configuring a Merge program



It should be emphasized that Mercurial by itself doesn't attempt
to do a Merge at the file level, neither does it make any
attempt to Resolve the conflicts.




By default, Mercurial will use the merge program defined by the
HGMERGE environment variable, or uses the one defined
in the mercurial.ini file. (see <a<br /> href="https://mercurial-scm.org/wiki/MergeProgram">MergeProgram
on the Mercurial Wiki for more information)



Reporting problems




Before you report any problems, please consult the <a<br /> href="https://mercurial-scm.org/">Mercurial web site
and see if your question is already in our list of <a<br /> href="https://mercurial-scm.org/wiki/FAQ">Frequently
Answered Questions (the "FAQ").




If you cannot find an answer to your question, please feel free
to send mail to the Mercurial mailing list, at <a<br /> href="mailto:mercurial@mercurial-scm.org">mercurial@mercurial-scm.org.
Remember, the more useful information you include in your
report, the easier it will be for us to help you!




If you are IRC-savvy, that's usually the fastest way to get
help. Go to #mercurial on irc.freenode.net.



Author and copyright information




Mercurial was written by http://www.selenic.com">Matt
Mackall, and is maintained by Matt and a team of volunteers.




The Windows installer was written by <a<br /> href="http://www.serpentine.com/blog">Bryan O'Sullivan.




Mercurial is Copyright 2005-2018 Matt Mackall and others. See
the Contributors.txt file for a list of contributors.




Mercurial is free software; you can redistribute it and/or
modify it under the terms of the <a<br /> href="http://www.gnu.org/licenses/old-licenses/gpl-2.0.txt">GNU
General Public License version 2 or any later version.




Mercurial is distributed in the hope that it will be useful, but
without any warranty; without even the implied warranty
of merchantability or fitness for a particular
purpose
. See the GNU General Public License for more
details.


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