view tests/revlog-formatv0.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

#!/usr/bin/env python
# Copyright 2010 Intevation GmbH
# Author(s):
# Thomas Arendsen Hein <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

"""Create a Mercurial repository in revlog format 0

changeset:   0:a1ef0b125355
tag:         tip
user:        user
date:        Thu Jan 01 00:00:00 1970 +0000
files:       empty
description:
empty file
"""

from __future__ import absolute_import
import binascii
import os
import sys

files = [
    (b'formatv0/.hg/00changelog.i',
     b'000000000000004400000000000000000000000000000000000000'
     b'000000000000000000000000000000000000000000000000000000'
     b'0000a1ef0b125355d27765928be600cfe85784284ab3'),
    (b'formatv0/.hg/00changelog.d',
     b'756163613935613961356635353036303562366138343738336237'
     b'61623536363738616436356635380a757365720a3020300a656d70'
     b'74790a0a656d7074792066696c65'),
    (b'formatv0/.hg/00manifest.i',
     b'000000000000003000000000000000000000000000000000000000'
     b'000000000000000000000000000000000000000000000000000000'
     b'0000aca95a9a5f550605b6a84783b7ab56678ad65f58'),
    (b'formatv0/.hg/00manifest.d',
     b'75656d707479006238306465356431333837353835343163356630'
     b'35323635616431343461623966613836643164620a'),
    (b'formatv0/.hg/data/empty.i',
     b'000000000000000000000000000000000000000000000000000000'
     b'000000000000000000000000000000000000000000000000000000'
     b'0000b80de5d138758541c5f05265ad144ab9fa86d1db'),
    (b'formatv0/.hg/data/empty.d',
     b''),
]

def makedirs(name):
    """recursive directory creation"""
    parent = os.path.dirname(name)
    if parent:
        makedirs(parent)
    os.mkdir(name)

makedirs(os.path.join(*'formatv0/.hg/data'.split('/')))

for name, data in files:
    f = open(name, 'wb')
    f.write(binascii.unhexlify(data))
    f.close()

sys.exit(0)