I'm using my OLPC XO-1 as a music server which allows anyone in the household the ability to play, stop, pause, adjust volume, and so on. This was first done by 'ssh olpc ...', but there's a substantial delay between issuing the action and its effect. So I wrote a simple web service that does the same thing. It turns out that most of the time is ssh overhead that's not present in a http connection.
$ time ssh olpc /home/olpc/bin/cmus-playpause real 0m0.522s $ time wget -O /dev/null http://olpc:8000/playpause real 0m0.066s
It's nothing like the 384x speedup I got the last time I was complaining about the olpc's performance, but it's still nothing to sneeze at.
I recently acquired a USB-connected relay that controls a standard power outlet, called the "USB NET POWER 8800". I'd ordered this with the knowledge that there was a Python implementation of the control program that was said to run on Linux.
It does work, but I was stunned at how long it took to switch the outlet on or off: a couple of seconds! I should disclaim that it's running on a rather underpowered machine (the OLPC XO-1 with a Geode x86 CPU @ 430MHz), but this was way too long to be acceptable:
$ time py-usbpower query Power: on real 0m2.690s user 0m1.484s sys 0m0.096sWith some detective work, I discovered that ctypes is doing things like running the compiler, objdump(!) and ldconfig(!), several times (!!), at each invocation of the program. (this is python2.5, but it looks like Python 2.7's ctypes still does essentially the same thing, unfortunately)
I set about to code this in C. For my reward, I got a very fast-executing program:
$ time c-usbpower status ON real 0m0.007s user 0m0.000s sys 0m0.000s
That's something like a 384x speedup. Lesson? ctypes has some very substantial startup costs for loading a library. It may be enough to make it unsuitable for a short-lived program.
In case it's useful to you, I enclose a copy of my usbpower program. It's under the terms of the GNU GPLv2.
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