[mythtv-users] Optimizing MythTV for AMD64

Kyle Rose krose+mythtv at krose.org
Sun Apr 3 15:21:40 UTC 2005

I posted the following on my homepage this morning:

I bought a dual Opteron 244 back in November of 2003 because I wanted a 
really, really fast desktop machine. Around the same time, I started 
playing with MythTV <http://www.mythtv.org/>, and it wasn't long after 
that I got a pcHDTV <http://www.pchdtv.com> HD-2000 card and began 
watching high-definition programming. Unfortunately, despite the 
Opteron's superior I/O bus design and incredibly speedy processing, it 
had more trouble decoding HDTV than did a much cheaper non-HT uniproc 
Pentium 4.

It has taken quite some time for MythTV to get to the point where it can 
reasonably be used with this configuration. Recently, a version of 
ffmpeg that appears to be optimized for AMD64 <http://www.x86-64.org/> 
has been imported into the Myth CVS repository: to get this, make sure 
to uncheck the "uselibmpeg" option in Setup/TV Settings/Playback. 
However, this alone isn't sufficient.

While I can't pinpoint the exact problem, I changed two major things in 
one day that resulted in much improved performance:

   1. /Cross/Downgraded from Debian <http://www.debian.org/> gcc-3.4 to
      Ubuntu <http://www.ubuntulinux.org/> Hoary./ This is a non-trivial
      operation if you are not used to screwing with Debian packages a
      lot. I still find old pieces of gcc-3.4/4.0-based packages now and
      then, and need to reinstall them from Ubuntu's archive when I find
      them. I recommend reinstalling from scratch if you aren't
      comfortable with recovering from broken libc packages by hand. :)
   2. /Upgraded my kernel to I actually don't think this was
      part of the performance improvement, but it was a variable, so I
      didn't want to leave it out. If you have stability problems with
      CONFIG_PREEMPT_BKL (preempting the big kernel lock), turn it off;
      I did.

In sum, my configuration looks like the following:

    * Hardware: Dual Opteron 244; Tyan <http://www.tyan.com/> Thunder
      K8W S2885 mobo w/AMD-81x1 I/O interfaces; NVidia
      <http://www.nvidia.com/> FX5600 AGP; 4 GB PC2700 (333MHz) dual DDR
      SDRAM; Creative <http://www.creative.com/> SB Live! 5.1 with coax
    * Distribution: Ubuntu Hoary
    * Linux: (See my kernel .config
    * ALSA drivers: 1.0.8 (alsa-source 1.0.8-4ubuntu4)
    * NVidia drivers: 7167 (nvidia-kernel-source 1.0.7167-0ubuntu25)
    * MythTV configuration: CVS as of 2005-Apr-02. Configuration
      options: --disable-audio-arts --disable-audio-jack --disable-lirc
      --disable-joystick-menu --disable-firewire --disable-ivtv
      --disable-xrandr --enable-opengl-vsync --enable-memalign-hack
    * MythTV patches: [broken pthread_rwlock_*

    * MythTV compilation: gcc-3.3, because the required Ubuntu packages
      (e.g., libGLU, libqt-mt) are compiled with gcc-3.3 and link with
      libstdc++5. I use make CC="gcc-3.3" CXX="g++-3.3" LINK="g++-3.3"
      to build.
    * MythTV config: turn off libmpeg decoding; use "ALSA:iec958" for
      the sound device; turn on AC3 passthrough; turn on extra audio

Performance improved significantly under this configuration. The 
following tests were performed with a playback window size of 1066x600 

    * Playback of a specific 1080i clip (CBS football) went from >99% of
      one CPU (with dropped frames) under the old config to ~55% of one
      CPU for mythfrontend and 15% for X.org with smooth playback.
    * Playback of a specific 720p clip (FOX "24") went from >99% of one
      CPU (with dropped frames) under the old config to ~40% of one CPU
      for mythfrontend and 15% for X.org with smooth playback.

Furthermore, at full size (1280x1024 with the video letterboxed to 
16:9), playback still runs smoothly, though 1080i playback consumes 
close to 100% of one CPU for mythfrontend. Not clear why the playback 
window size should matter with XVideo, but it does.

If you have success with this configuration, I'd love to hear about it. 
If you have problems and are able to determine what I've left out, let 
me know so I can add the appropriate config elements.


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