Playing with CHDK

I've spent the morning playing with my Canon PowerShot SD870 IS, loading the Canon Hacker Development Kit on it. I ran through this quick introduction.  So now I should be able to write a script to do some hi-fi kite aerial photography!  It'll complement my arduino-controlled cheap-o camera nicely, I think.

LED Flex Strip Test

My boss understands me -- so he got me a meter of LED Flex Strip from adafruit.  Here's the first test of having Arduino control it.  It's autonomous, actually, and the USB connection is only for power.  That means I could, say, pin it to my bag with a battery pack and have it tell me the current temperature.  Or something.

Learning Python (Fourth Edition)

Well, I'm only two chapters in to Learning Python, but I'm finding it very interesting. (Happily, Mac OS X has version 2.6, these days.) I picked python partially because Google uses it so extensively -- but it also seems to be handy in general.  I just keep seeing it everywhere.

When I started learning perl, ages ago, it really opened up a lot of new intellectual opportunities for me.  With perl, if I had a text stream, I could parse and extract from it -- and everything was text then!  I'm hoping Python will be an "enabling" kind of thing like that too, but up to date for the now.  Here goes....

Linux, Swap and Render Farms

The debate occurred again last night, with a Cinematics group, about how best to configure their linux render nodes.  We're running a bare metal hypervisor, with two guests running RHEL 5, on a pair of xeon 5520 processors, with  12 Gb RAM and a slow-mo SATA disk.  How should we allocate RAM to the guests, and do we want swap?

Sven immediately offered this article on how mysql behaves on a NUMA CPU architecture, which suggests to me that I might as well turn swap off.  The counterpoint (and traditional view) is that a linux machine must have swap, as a part of its normal modus operandi.  So far, the render nodes show no difference with/without swap (so I turned it off) and two virtual guests outperform one OS running on bare metal.  I suspect the virtualization layer is sticking one guest on each of the processors, so their RAM is staying local to the CPU they're on.

I don't know the answer, but it's gonna be interesting.  If you're in the same boat, you'll appreciate this handy secret-decoder-ring for vmstat.  And here's a primer on "swappiness."  Also, here's the middle road solution, enable swap, but just a pittance of it.

 Finally, if you're running a render/compute farm, you'll find these bits handy ... there's a lovely o'reilly article on how the linux out-of-memory killer works.  You'll also be interested in this article on how linux memory overcommit works.  And finally, if you're trying with and without swap, here's a quick bit on how to use a normal file as swap, so you donut have to repartition anything to test the on/off configs.

Hopefully this helps someone!