[mythtv-users] Epia-M10K (Nehemiah) software mpeg2 decoder performance

Mikhail D'Vane mikhaildvane at hotmail.com
Tue Feb 24 21:53:47 EST 2004


I have set up an Epia-M10000 (Nehemiah) as a mythtv remote
frontend.  Unfortunately, the system has a problem that I have
been trying to debug for months (literally).

My problem is that when using software mpeg2 decoding (encoded
with a PVR-250 on my backend system), the CPU utilization for
the frontend jumps to ~100%.  This results in very poor playback
performance (crackly audio, periodic video pauses).

Here's the odd thing, though - I know that the Nehemiah can
handle mpeg2 software decoding at the resolution/bit rate I have
set (480x480, 4500/6000max bitrate).  I know this because I have
set up a system for a friend with the exact same motherboard type.

Here's the quick background story....

Orignally, I setup a mythtv system on a 1Ghz PentiumIII system
that I had spare.   I used RH9.0 and followed Jarod's (extremely
well-written) install guide using rpms maintained by Axel Thimm.
My friend liked the system so much he asked me to build him one.
However, he didn't have a spare system, so we bought all new
components and I built a mythtv system (frontend/backend combined)
around an Epia-10K for him.  This system was also using RH9.0,
but I had to deviate significantly from Jarod (and Axel's)
configuration because the Via binary drivers only worked against
the stock RH9.0 kernel.

Once I had my friend's system working, I liked it so much I decided
to invest in an Epia-10k for myself.  I followed the same setup
routine as before, but I ran into this performance problem.  Playing
the same file, my system pegs at 100% cpu (used by mythfrontend)
while my friend's hums along at about 50%.

Here's the information on my (and my friend's) system:

RH9.0 stock kernel (2.4.20-8)
ALSA v0.9.8 (using OSS emulation)
Software mpeg decoding (not using viaslice)
Stock RH9.0 Xfree (4.3.0?)
Via binaries 40037 (Xfree, kernel modules)

I have tried the following to try to alleviate this problem:

- enable "extra audio buffering" - still at 100% CPU, audio fine,
  but everything pauses at 2 sec intervals (prebuffering pause)
- try different versions of mythtv (tried 0.13 and 0.14)
- upgrade Via binaries to 40038 package
- run with Native ALSA
- upgrade ALSA to later revision (1.0-pre3)
- use open-source versions of Via binaries
- Add "pci_retry=true" to the Devices section of my XF86Config file
- Ensured that v4l and dri Xfree modules are loading (glxgears ~380fps)
- Corrected the incorrect MTRR settings set by XFree for the Epia HW
- Ensured that both systems are running same bios (1.0F) and have same
  bios settings
- Ensured that dxs_support=3 is set for the snd-via82xx in modules.conf
- Ensured that my HDD is using DMA (hdparm -d /dev/hda says using
  DMA is ON)
- Changed Linux distribution from RH9.0 to Gentoo 1.4
  (running 2.4.24-epia1 kernel)
- Built everything (mythtv, ALSA, etc) from source (pretty easy
  with Gentoo ebuilds)
- Upgraded Xfree to Epia-centric version per Rroet's "Gentoo on Epia"
  install guide

None of the above made any difference in my playback performance.

The only thing that makes my Epia system usable is to using the Epia's
onboard MPEG decoder.  The playback is then smooth (mythfrontend using 
but the system is not as stable as I would like.

Also, there are some minor differences between my system and my
friend's.  They are:

- All his filesystems are ext2, mine are ext3 (boot) and reiserfs
  (root and video partitions)
- His system was setup with Axel's mythtv-0.12 distribution while mine
  was (initially) setup with Axel's mythtv-0.13 distribution and
  downgraded to 0.12

Also, both systems have the same CPU utilization (~30%) when playing
back DVDs with Xine.

Does anyone have any additional pointers for me to try?  I saw a message
from Isaac to Tako regarding Tako's high Nehemiah CPU utilization, but
I never saw a post on a resolution.

At this point, I'm considering cloning my friend's HDD to see if putting
his exact software on my hardware resolves the issue.

That... or using the onboard mpeg decoder and dealing with the lower

Thanks for any help and also thanks for reading this (long-winded) email.


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