Set up SSH Mulitplexing for Speed
=================================

This is one of my most convenient tricks. The slowest parts of `git pull` and
`git push` are starting up the SSH connection. However, there is a way to
eliminate this problem simply by opening a persistent tunnel, which `git pull`
and `git push` automatically reuse.

~/.ssh/config
-------------

Enter the ControlMaster option for OpenSSH. 

_________________________
*ControlMaster*

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 *ControlPath* with *ControlMaster* set to “no”
(the default).

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.

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 *ControlPath* cannot be opened, ssh will
continue without connecting to a master instance.

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.

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.
_________________________

So I set up my ~/.ssh/config as follows.

[source,bash,numbered]
#~/.ssh/config
ControlMaster auto
ControlPath ~/.ssh/pool/%r@%h
ServerAliveCountMax 6
ServerAliveInterval 10
TCPKeepAlive yes

And we're set!.

First, a few benchmarks
-----------------------

First, lets see how fast it is without the magic:

[source,bash]
------
> time for i in $( seq 0 10 ) ; do git fetch github; done

real	0m47.798s
user	0m0.226s
sys	0m0.236s

> time for i in $( seq 0 10 ) ; do git fetch origin; done

real	0m48.444s
user	0m0.235s
sys	0m0.250s
------

Averaging about 4.34s per fetch to Github, 4.40s to gentoo overlays. 

SLOOW.

Start a background connection
-----------------------------

With ControlMaster, you set up a long-lived SSH connection.

[source,bash]
------
> ssh -fNn git@github.com
> ssh -fNn git@git.gentoo.org
------

And we're truely really to start cooking with petrol.

Post Configuration Benchmarks
-----------------------------

[source,bash]
------
> time for i in $( seq 0 10 ) ; do git fetch github; done

real	0m12.935s
user	0m0.093s
sys	0m0.193s

> time for i in $( seq 0 10 ) ; do git fetch origin; done

real	0m11.597s
user	0m0.099s
sys	0m0.191s
------

O_o. Averaging about 1.175s and 1.05s respectively.