[mythtv] ringbuffer.cpp

Jonas Arndt jonas.arndt at thearndtfamily.com
Mon Feb 17 01:58:01 UTC 2014

On 02/15/2014 08:05 PM, Jean-Yves Avenard wrote:
> On 16 February 2014 09:36, Warpme <warpme at o2.pl> wrote:
>> This is also how I understand things. I think there is somewhere bug.
>> But we don't know yet in which part of data path it is.
>> That's why I propose to start with simplest possible data path as it has
>> lower number of variables to check.
> downgraded to 3.2 original 12.04 kernel; using your sysconf values and
> the issue occurred again in liveTV; another 20+ seconds lock in the
> ringbuffer trying to read the data.
> iperf on the dedicated internel link ; I get 993Mbit/s between the
> backend machine and the NFS server.
> Using dd if=/dev/zero of=/path/to/nfs bs=4k count=1M; I get 104MB/s
> Using a little unit test with 4 simultaneous TFW; I get 75MB/s on that drive...
> I don't see how their could be a bottleneck occurring watching a
> single 12Mbit/s DVB-T stream...
I had an interesting observation over the weekend. I installed a replica 
of my configuration for a friend. He only has a single front-end though. 
Ubuntu 12.04 on both back-end and front-end. The front-end runs on a 
ZBox ID11 (just like my front-ends). For some reason my friend had 
freezes occurring every 5-10 minutes and the front-end mostly couldn't 
recover. I had even put JY's patch on the back-end but that did not 
help. I started doing some network pinging to the back-end and other 
machines on the network. Whenever the back-end was streaming Live TV I 
got some network latency. From the back-end I would mostly have around 
0.100 ms replies but then every couple of seconds I would get 7-8 ms 
replies. This weird behavior would stop once I stopped watching live tv 
(ping would be rock solid again). This would not happen on my system at 
home where I would have 0 latency even when watching live TV. After some 
troubleshooting it turns out that his server only had a 100 Mbps NIC 
while mine had a 1 Gbps. I installed a 1 Gbps card in his server and the 
problem is gone. It still freezes up a second or so between shows, but I 
have that as well.

Now why on earth would I need 1 Gbps to run watch liveTV? No issues with 
recorded shows on the 100 Mbit NIC. I don't know much about the Myth 
streaming protocol but it seems there is stuff going on there for LiveTV 
that would require a much larger bandwidth then one would expect.


// Jonas

More information about the mythtv-dev mailing list