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<div id="header">
<h1>Set up SSH Mulitplexing for Speed</h1>
<div id="toc">
<div id="toctitle">Table of Contents</div>
<noscript><p><b>JavaScript must be enabled in your browser to display the table of contents.</b></p></noscript>
</div>
</div>
<div id="content">
<div id="preamble">
<div class="sectionbody">
<div class="paragraph"><p>This is one of my most convenient tricks. The slowest parts of <tt>git pull</tt> and
<tt>git push</tt> are starting up the SSH connection. However, there is a way to
eliminate this problem simply by opening a persistent tunnel, which <tt>git pull</tt>
and <tt>git push</tt> automatically reuse.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_ssh_config">1. ~/.ssh/config</h2>
<div class="sectionbody">
<div class="paragraph"><p>Enter the ControlMaster option for OpenSSH.</p></div>
<div class="quoteblock">
<div class="content">
<div class="paragraph"><p><strong>ControlMaster</strong></p></div>
<div class="paragraph"><p>Enables the sharing of multiple sessions over a single network connection.
When set to “yes”, ssh(1) will listen for connections on a control socket
specified using the ControlPath argument. Additional sessions can connect to
this socket using the same <strong>ControlPath</strong> with <strong>ControlMaster</strong> set to “no”
(the default).</p></div>
<div class="paragraph"><p>These sessions will try to reuse the master instance’s network connection
rather than initiating new ones, but will fall back to connecting normally if
the control socket does not exist, or is not listening.</p></div>
<div class="paragraph"><p>Setting this to “ask” will cause ssh to listen for control connections, but
require confirmation using the SSH_ASKPASS program before they are accepted
(see ssh-add(1) for details). If the <strong>ControlPath</strong> cannot be opened, ssh will
continue without connecting to a master instance.</p></div>
<div class="paragraph"><p>X11 and ssh-agent(1) forwarding is supported over these multiplexed
connections, however the display and agent forwarded will be the one belonging
to the master connection i.e. it is not possible to forward multiple displays
or agents.</p></div>
<div class="paragraph"><p>Two additional options allow for opportunistic multiplexing: try to use a
master connection but fall back to creating a new one if one does not already
exist. These options are: “auto” and “autoask”. The latter requires
confirmation like the “ask” option.</p></div>
</div>
<div class="attribution">
</div></div>
<div class="paragraph"><p>So I set up my ~/.ssh/config as follows.</p></div>
<div class="listingblock">
<div class="content"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre>1
2
3
4
5
6</pre></div></td><td class="code"><div class="highlight"><pre><span class="c">#~/.ssh/config</span>
ControlMaster auto
ControlPath ~/.ssh/pool/%r@%h
ServerAliveCountMax 6
ServerAliveInterval 10
TCPKeepAlive yes
</pre></div>
</td></tr></table></div></div>
<div class="paragraph"><p>And we’re set!.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_first_a_few_benchmarks">2. First, a few benchmarks</h2>
<div class="sectionbody">
<div class="paragraph"><p>First, lets see how fast it is without the magic:</p></div>
<div class="listingblock">
<div class="content"><div class="highlight"><pre>> <span class="nb">time </span><span class="k">for </span>i in <span class="k">$(</span> seq 0 10 <span class="k">)</span> ; <span class="k">do </span>git fetch github; <span class="k">done</span>
real 0m47.798s
user 0m0.226s
sys 0m0.236s
> <span class="nb">time </span><span class="k">for </span>i in <span class="k">$(</span> seq 0 10 <span class="k">)</span> ; <span class="k">do </span>git fetch origin; <span class="k">done</span>
real 0m48.444s
user 0m0.235s
sys 0m0.250s
</pre></div></div></div>
<div class="paragraph"><p>Averaging about 4.34s per fetch to Github, 4.40s to gentoo overlays.</p></div>
<div class="paragraph"><p>SLOOW.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_start_a_background_connection">3. Start a background connection</h2>
<div class="sectionbody">
<div class="paragraph"><p>With ControlMaster, you set up a long-lived SSH connection.</p></div>
<div class="listingblock">
<div class="content"><div class="highlight"><pre>> ssh -fNn git@github.com
> ssh -fNn git@git.overlays.gentoo.org
</pre></div></div></div>
<div class="paragraph"><p>And we’re truely really to start cooking with petrol.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_post_configuration_benchmarks">4. Post Configuration Benchmarks</h2>
<div class="sectionbody">
<div class="listingblock">
<div class="content"><div class="highlight"><pre>> <span class="nb">time </span><span class="k">for </span>i in <span class="k">$(</span> seq 0 10 <span class="k">)</span> ; <span class="k">do </span>git fetch github; <span class="k">done</span>
real 0m12.935s
user 0m0.093s
sys 0m0.193s
> <span class="nb">time </span><span class="k">for </span>i in <span class="k">$(</span> seq 0 10 <span class="k">)</span> ; <span class="k">do </span>git fetch origin; <span class="k">done</span>
real 0m11.597s
user 0m0.099s
sys 0m0.191s
</pre></div></div></div>
<div class="paragraph"><p>O_o. Averaging about 1.175s and 1.05s respectively.</p></div>
</div>
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Last updated 2012-04-02 04:30:04 NZST
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