We all hate the A in ADSL, but most of us are stuck with it. So there
are any number of workarounds that keep our link to the Internet
working with a certain amount of perceived fluidity, by way of
"traffic shaping". Many of us use
wondershaper for that purpose:
it's a magic tool that keeps the latency low for interactive traffic
by ensuring that the bulk traffic doesn't interfere too much with it.
We all hate the A in ADSL, but most of us are stuck with it. So there are any number of workarounds that make the establishment of new connections to external servers feel faster. Many of us use the SSH "ControlMaster" series of options for that purpose: it's a set of options that allow new connections to a server to reuse an existing one if there is already a connection open (or if there was one until not too long ago), so some time is saved becaused the handshake to establish the connection is only needed once.
Now combine both. SSH to an external server, for instance, work on
it. Since it's meant to be an interactive connection,
set some appropriate flags on the IP packets, and
give these packets priority over whatever bulk traffic is happening at
the time. At some point, you realise you need to transfer a large set
of files to there, so you start an SCP transfer.
scp, being part of
the SSH suite, will reuse the existing connection. Suddenly, your
bulk transfer will not only get priority over the other kinds of
traffic you might have, but also get intermingled with your keystrokes
slogin session to the same server. Which means your
keystrokes will be delayed significantly, and working interactively
becomes even more of a pain. In my case, the priority boost given to
the SCP transfer is sometimes enough to cause other unrelated sockets
to time out.
After reading some docs, I found my solution. It isn't much, but it's going to change my way of working significantly enough that I'm going to share it anyway.
alias scp='scp -oControlPath=none'
Also, since I use
dput extensively, and it invokes
scp in many
cases without reusing my shell aliases, part of my
[DEFAULT] ssh_config_options = ControlPath=none […]
This means I keep the advantages of traffic shaping for interactive sessions, but SCP stuff won't interfere anymore, and I can continue working on the server while the new version of the packages that I need to get there are in transit.
One small improvement at a time, progress!Posted jeu. 25 août 2011 00:00:00 CEST