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view mercurial/diffhelper.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 | 86e7a57449fa |
children | e7aa113b14f7 |
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# diffhelper.py - helper routines for patch # # Copyright 2009 Matt Mackall <mpm@selenic.com> and others # # This software may be used and distributed according to the terms of the # GNU General Public License version 2 or any later version. from __future__ import absolute_import from .i18n import _ from . import ( error, ) def addlines(fp, hunk, lena, lenb, a, b): """Read lines from fp into the hunk The hunk is parsed into two arrays, a and b. a gets the old state of the text, b gets the new state. The control char from the hunk is saved when inserting into a, but not b (for performance while deleting files.) """ while True: todoa = lena - len(a) todob = lenb - len(b) num = max(todoa, todob) if num == 0: break for i in xrange(num): s = fp.readline() if not s: raise error.ParseError(_('incomplete hunk')) if s == "\\ No newline at end of file\n": fixnewline(hunk, a, b) continue if s == '\n' or s == '\r\n': # Some patches may be missing the control char # on empty lines. Supply a leading space. s = ' ' + s hunk.append(s) if s.startswith('+'): b.append(s[1:]) elif s.startswith('-'): a.append(s) else: b.append(s[1:]) a.append(s) def fixnewline(hunk, a, b): """Fix up the last lines of a and b when the patch has no newline at EOF""" l = hunk[-1] # tolerate CRLF in last line if l.endswith('\r\n'): hline = l[:-2] else: hline = l[:-1] if hline.startswith((' ', '+')): b[-1] = hline[1:] if hline.startswith((' ', '-')): a[-1] = hline hunk[-1] = hline def testhunk(a, b, bstart): """Compare the lines in a with the lines in b a is assumed to have a control char at the start of each line, this char is ignored in the compare. """ alen = len(a) blen = len(b) if alen > blen - bstart or bstart < 0: return False for i in xrange(alen): if a[i][1:] != b[i + bstart]: return False return True