[mythtv-users] Secrets for low powered front ends ?

Matt Garman matthew.garman at gmail.com
Thu Oct 13 02:44:52 UTC 2011

My take on this is that it's one of those situations that boils down
to three criteria, but you can have only two.  In this case: low power
usage, high compute performance, low cost.  Pick any two.

I chose to go with low power and high compute performance, which for
me was Intel's Sandy Bridge (SNB).  With the distro I'm using
(CentOS), Sandy Bridge graphics support isn't yet in the "just works"
category.  But from what I've read, it seems it's at least fairly
reliable on more bleeding edge distros and/or if you're willing to
spend some futzing time.

My goal was primarily low power, but I also wanted a minimum of
tweaking, configuring, fighting, etc.  I wanted as close as possible
to "just works".  And my take on MythTV is that software decoding is
what "just works" out of the box---so get a super fast CPU, and time
spent futzing should be minimized.  As I suggested, SNB graphics isn't
yet in the "just works" category, so I threw in a GT-430.
Nvidia/vdpau setup isn't *that* much extra work, and it's so popular
that it's very well supported in the community.  But it does add about
10 watts to my idle AC power consumption, and adds more heat to the
box.  But as soon as the SNB graphics support for CentOS matures, I'm
hoping to drop the discrete GPU, and save on power, heat, and
configuration complexity.

Before I built this system, I tried to research if the CPU I bought
(i5-2500k) would be powerful enough to do software decoding of
anything I could possibly throw at it.  Since I'm using vdpau, I
haven't been able to test this.  However, this[1] was one of the most
interesting threads I read in my research.  The choice quote, emphasis
mine: "My Core i7 920 (2.6 Ghz) can *almost* play back [Transformers:
Revenge of the Fallen single-sliced BluRay on] a single core with
software decoding (some part work fine, but some are choppy)."  My SNB
CPU is faster in terms of clock speed and a newer architecture, which
the benchmarks suggest is superior.

I did a writeup of my build on Silent PC Review[2] if you're curious.
Without the GT-430, my idle AC power consumption is about 24 watts.
With choice hardware, I've seen a number of SNB builds online that
actually idle at less than 20 watts---this is competitive with the
idle power consumption of Atom, but you have a "real" CPU when you
need it.  As soon as SNB graphics on Linux gets to the "just works"
stage, I don't know why anyone would choose Atom+ION, other than for
cost reasons.  And to be clear, I'm not even talking about the
upcoming SNB GPU-based hardware codec support---I'm talking about SNB
graphics working strictly as a display driver, and all "real work"
being done in software through the CPU portion of the package.
Furthermore, once I can drop the discrete graphics, I can actually use
a smaller case, and compete with Atom in terms of size and silence.

[1] mythtv-users list, "Why does playback only use 1 core on some
BluRay movies?", Nov 2009

[2] Silent PC Review General Gallery Forum, "new htpc - q11b,
i5-2500k, axp-140, gt430, picoPSU"

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