view doc/gendoc.py @ 35793:4fb2bb61597c

bundle2: increase payload part chunk size to 32kb

Bundle2 payload parts are framed chunks. Esentially, we obtain
data in equal size chunks of size `preferedchunksize` and emit those
to a generator. That generator is fed into a compressor (which can
be the no-op compressor, which just re-emits the generator). And
the output from the compressor likely goes to a file descriptor
or socket.

What this means is that small chunk sizes create more Python objects
and Python function calls than larger chunk sizes. And as we know,
Python object and function call overhead in performance sensitive
code matters (at least with CPython).

This commit increases the bundle2 part payload chunk size from 4k
to 32k. Practically speaking, this means that the chunks we feed
into a compressor (implemented in C code) or feed directly into a
file handle or socket write() are larger. It's possible the chunks
might be larger than what the receiver can handle in one logical
operation. But at that point, we're in C code, which is much more
efficient at dealing with splitting up the chunk and making multiple
function calls than Python is.

A downside to larger chunks is that the receiver has to wait for that
much data to arrive (either raw or from a decompressor) before it
can process the chunk. But 32kb still feels like a small buffer to
have to wait for. And in many cases, the client will convert from
8 read(4096) to 1 read(32768). That's happening in Python land. So
we cut down on the number of Python objects and function calls,
making the client faster as well. I don't think there are any
significant concerns to increasing the payload chunk size to 32kb.

The impact of this change on performance significant. Using `curl`
to obtain a stream clone bundle2 payload from a server on localhost
serving the mozilla-unified repository:

before: 20.78 user; 7.71 system;  80.5 MB/s
after:  13.90 user; 3.51 system; 132 MB/s
legacy:  9.72 user; 8.16 system; 132 MB/s

bundle2 stream clone generation is still more resource intensive than
legacy stream clone (that's likely because of the use of a
util.chunkbuffer). But the throughput is the same. We might
be in territory we're this is effectively a benchmark of the
networking stack or Python's syscall throughput.

From the client perspective, `hg clone -U --stream`:

before: 33.50 user; 7.95 system; 53.3 MB/s
after:  22.82 user; 7.33 system; 72.7 MB/s
legacy: 29.96 user; 7.94 system; 58.0 MB/s

And for `hg clone --stream` with a working directory update of
~230k files:

after:  119.55 user; 26.47 system; 0:57.08 wall
legacy: 126.98 user; 26.94 system; 1:05.56 wall

So, it appears that bundle2's stream clone is now definitively faster
than legacy stream clone!

Differential Revision: https://phab.mercurial-scm.org/D1932

#!/usr/bin/env python
"""usage: %s DOC ...

where DOC is the name of a document
"""

from __future__ import absolute_import

import os
import sys
import textwrap

# This script is executed during installs and may not have C extensions
# available. Relax C module requirements.
os.environ['HGMODULEPOLICY'] = 'allow'
# import from the live mercurial repo
sys.path.insert(0, "..")
from mercurial import demandimport; demandimport.enable()
# Load util so that the locale path is set by i18n.setdatapath() before
# calling _().
from mercurial import util
util.datapath
from mercurial import (
    commands,
    extensions,
    help,
    minirst,
    ui as uimod,
)
from mercurial.i18n import (
    gettext,
    _,
)

table = commands.table
globalopts = commands.globalopts
helptable = help.helptable
loaddoc = help.loaddoc

def get_desc(docstr):
    if not docstr:
        return "", ""
    # sanitize
    docstr = docstr.strip("\n")
    docstr = docstr.rstrip()
    shortdesc = docstr.splitlines()[0].strip()

    i = docstr.find("\n")
    if i != -1:
        desc = docstr[i + 2:]
    else:
        desc = shortdesc

    desc = textwrap.dedent(desc)

    return (shortdesc, desc)

def get_opts(opts):
    for opt in opts:
        if len(opt) == 5:
            shortopt, longopt, default, desc, optlabel = opt
        else:
            shortopt, longopt, default, desc = opt
            optlabel = _("VALUE")
        allopts = []
        if shortopt:
            allopts.append("-%s" % shortopt)
        if longopt:
            allopts.append("--%s" % longopt)
        if isinstance(default, list):
            allopts[-1] += " <%s[+]>" % optlabel
        elif (default is not None) and not isinstance(default, bool):
            allopts[-1] += " <%s>" % optlabel
        if '\n' in desc:
            # only remove line breaks and indentation
            desc = ' '.join(l.lstrip() for l in desc.split('\n'))
        desc += default and _(" (default: %s)") % default or ""
        yield (", ".join(allopts), desc)

def get_cmd(cmd, cmdtable):
    d = {}
    attr = cmdtable[cmd]
    cmds = cmd.lstrip("^").split("|")

    d['cmd'] = cmds[0]
    d['aliases'] = cmd.split("|")[1:]
    d['desc'] = get_desc(gettext(attr[0].__doc__))
    d['opts'] = list(get_opts(attr[1]))

    s = 'hg ' + cmds[0]
    if len(attr) > 2:
        if not attr[2].startswith('hg'):
            s += ' ' + attr[2]
        else:
            s = attr[2]
    d['synopsis'] = s.strip()

    return d

def showdoc(ui):
    # print options
    ui.write(minirst.section(_("Options")))
    multioccur = False
    for optstr, desc in get_opts(globalopts):
        ui.write("%s\n    %s\n\n" % (optstr, desc))
        if optstr.endswith("[+]>"):
            multioccur = True
    if multioccur:
        ui.write(_("\n[+] marked option can be specified multiple times\n"))
        ui.write("\n")

    # print cmds
    ui.write(minirst.section(_("Commands")))
    commandprinter(ui, table, minirst.subsection)

    # print help topics
    # The config help topic is included in the hgrc.5 man page.
    helpprinter(ui, helptable, minirst.section, exclude=['config'])

    ui.write(minirst.section(_("Extensions")))
    ui.write(_("This section contains help for extensions that are "
               "distributed together with Mercurial. Help for other "
               "extensions is available in the help system."))
    ui.write(("\n\n"
             ".. contents::\n"
             "   :class: htmlonly\n"
             "   :local:\n"
             "   :depth: 1\n\n"))

    for extensionname in sorted(allextensionnames()):
        mod = extensions.load(ui, extensionname, None)
        ui.write(minirst.subsection(extensionname))
        ui.write("%s\n\n" % gettext(mod.__doc__))
        cmdtable = getattr(mod, 'cmdtable', None)
        if cmdtable:
            ui.write(minirst.subsubsection(_('Commands')))
            commandprinter(ui, cmdtable, minirst.subsubsubsection)

def showtopic(ui, topic):
    extrahelptable = [
        (["common"], '', loaddoc('common')),
        (["hg.1"], '', loaddoc('hg.1')),
        (["hg-ssh.8"], '', loaddoc('hg-ssh.8')),
        (["hgignore.5"], '', loaddoc('hgignore.5')),
        (["hgrc.5"], '', loaddoc('hgrc.5')),
        (["hgignore.5.gendoc"], '', loaddoc('hgignore')),
        (["hgrc.5.gendoc"], '', loaddoc('config')),
    ]
    helpprinter(ui, helptable + extrahelptable, None, include=[topic])

def helpprinter(ui, helptable, sectionfunc, include=[], exclude=[]):
    for names, sec, doc in helptable:
        if exclude and names[0] in exclude:
            continue
        if include and names[0] not in include:
            continue
        for name in names:
            ui.write(".. _%s:\n" % name)
        ui.write("\n")
        if sectionfunc:
            ui.write(sectionfunc(sec))
        if callable(doc):
            doc = doc(ui)
        ui.write(doc)
        ui.write("\n")

def commandprinter(ui, cmdtable, sectionfunc):
    h = {}
    for c, attr in cmdtable.items():
        f = c.split("|")[0]
        f = f.lstrip("^")
        h[f] = c
    cmds = h.keys()
    cmds.sort()

    for f in cmds:
        if f.startswith("debug"):
            continue
        d = get_cmd(h[f], cmdtable)
        ui.write(sectionfunc(d['cmd']))
        # short description
        ui.write(d['desc'][0])
        # synopsis
        ui.write("::\n\n")
        synopsislines = d['synopsis'].splitlines()
        for line in synopsislines:
            # some commands (such as rebase) have a multi-line
            # synopsis
            ui.write("   %s\n" % line)
        ui.write('\n')
        # description
        ui.write("%s\n\n" % d['desc'][1])
        # options
        opt_output = list(d['opts'])
        if opt_output:
            opts_len = max([len(line[0]) for line in opt_output])
            ui.write(_("Options:\n\n"))
            multioccur = False
            for optstr, desc in opt_output:
                if desc:
                    s = "%-*s  %s" % (opts_len, optstr, desc)
                else:
                    s = optstr
                ui.write("%s\n" % s)
                if optstr.endswith("[+]>"):
                    multioccur = True
            if multioccur:
                ui.write(_("\n[+] marked option can be specified"
                           " multiple times\n"))
            ui.write("\n")
        # aliases
        if d['aliases']:
            ui.write(_("    aliases: %s\n\n") % " ".join(d['aliases']))


def allextensionnames():
    return extensions.enabled().keys() + extensions.disabled().keys()

if __name__ == "__main__":
    doc = 'hg.1.gendoc'
    if len(sys.argv) > 1:
        doc = sys.argv[1]

    ui = uimod.ui.load()
    if doc == 'hg.1.gendoc':
        showdoc(ui)
    else:
        showtopic(ui, sys.argv[1])