[mythtv-users] DVB problems after system update

Johan Reinalda johan at global.thunderbird.edu
Fri Dec 22 16:27:08 UTC 2006


I just updated my FC6-x86_64 system to the latest patches and the latest 
myth rpms (0.20-148). (I am now running kernel 2.6.18-1.2868, on AMD64/2800, 
with 768MB)

I am now experiencing a number of problems with my DVB-S, but NOT with my 

- I get "hickups" while watching live Sat. TV; the picture freezes 
momentarily, then continues.
- on Sat. recordings, I get lots of jumps, where the recording simply misses 
several seconds

In the backend log, I see the following lines
     DevRdB(0) Error: Driver buffers overflowed

and the front end log show things like:
NVP: prebuffering pause
RingBuf(/mnt/store/recordings/2153_20061221210417.mpg): Taking too long to 
be allowed to read..
RingBuf(/mnt/store/recordings/2153_20061221210417.mpg): Waited 1.0 seconds 
for data to become available...

This seems to mean disk access issues? However, my disk and its partitions 
are running on a 3Ware 8006 raid1 controller with dual SATA150 drives, and 
hdparm testing show performace as expected.  (mythfrontend is also running 
as suid root)

I did some other testing, to see if I can eliminate the base system. When I 
run the following in three different shells, basically simulating what myth 
live tv does, the picture is just fine:

szap   #tune the DVB card

cat /dev/dbv/adapter0/dvr0 > /mnt/store/FILE.mpg      #record from dvb-s 
card to file

mplayer /mnt/store/FILE.mpg  #play file while being 'recorded'

Cpu utilization with the above 3 is about 10%, with Myth Livetv it's about 

I've notived that vmstat shows virtually no disk waits (WA value) when I run 
things in the 3 shells, but with Mythtv I see this jump from 1 to as high as 
6 at times.

I have backed down to the original kernel, build 2798, and to myth 
0.20.-147.1 with the same results; the szap/cat/mplayer test works fine 
under 2.6.18-2798. Nvidia 5200 drivers are v8776

Now I am starting to expect something else, like QT libraries, or some other 
piece that got upgraded?

Any suggestions?



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