viernes, agosto 05, 2011

Building my own NAS for DLNA (IV): CPU usage and power consumption

Well, seeing that streaming works fine on these two platforms, we should see how efficient they are. Serviio works by scanning the folders every 5 minutes (default, configurable value) and generating the data needed for future streaming in a TEMP directory. I suppose that in that way the job is ready when streaming starts. One problem I see with that approach is what happens if a scan starts with new files in the folders being processed while you're watching some content. The only thing I can say is that I still haven't had this issue.

CPU usage

To see how much CPU is used while scanning/preparing the files, I started Performance Monitor and Resource Monitor to check the general CPU usage and what processes were involved.

While idling, the CPU usage is between 4-5% in all cases, but transcoding changes it all. Serviio uses FFMPEG to do the actual work, and the problem is that this is not a multi-threaded process. This result in transcoding not consuming all CPU resources available in the Atom (2 logical cores), while the Pentium M (mono-core) reaches almost 100% CPU usage. Well, this has two consequences: first, the Atom could do other tasks while transcoding without suffering so much; second, as transcoding tend to scale very well with megahertz and/or CPU usage, we should expect shorter transcoding times in the Pentium M. While streaming the Atom consumes 5% more of CPU than the Pentium M.

I measure how long it took to transcode the two episodes of Top Gear (about 2.9 GB) in both machines, and the Atom one took 3 times as long as the Pentium M (400 seconds vs about 130).

Power consumption

The screen was open while testing, but when I closed it the consumption dropped 4 watts in the Pentium M and 1 watt in the Atom, an indicator of how efficient panels have become. As the PC will be headless most of the tim,e I'm using the values excluding this consumption.

The first thing to notice is that the Atom's consumption is below 2 watts, from idle to transcoding, while the Pentium M consumes 4 times the power while working hard. The fan also speeded up, making some noise. Streaming raises the consumption about 50% in the Pentium M.

Next (and last) chapter, conclusions.

Building my own NAS for DLNA (I)
Building my own NAS for DLNA (II): specs
Building my own NAS for DLNA (III): performance
Building my own NAS for DLNA (IV): CPU usage and power consumption
Building my own NAS for DLNA (V): Conclusions

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