[mythtv-users] Commercial flagging on backend disrupts HDTV playback on front end

William Powers wepprop at sbcglobal.net
Mon Sep 10 23:57:35 UTC 2007

Taco Mel wrote:
> With my current settings I have experienced a problem
> with playing back HDTV (prebuffer pauses, very
> jittery) when the back end server is "busy":
> 1. Recording HDTV stream with pcHDTV 5500
> 2. Recording SDTV stream with Hauppauge 500
> 3. Commercial flagging #1 and #2
> 4. Feeding HDTV stream #1 to remote front end
> The back end has 1 TB storage in RAID-5 and is a dual
> Xeon 1.8 GHz setup, hyperthreading enabled.  Linux
> sees this as 4 CPU's.  There I find a "mythcommflag"
> process using 100% of a CPU (iowait around 5-20%). 
> The front end (Athlon X2 5200+) isn't even breaking a
> sweat. I tried to "renice" the mythcommflag process to
> +19 on the back end and this did not help.  Killing
> mythcommflag on the back end immediately "fixed" the
> problem.
> While it's easy enough for me to log in to the back
> end to kill the commercial flagging, I'd like
> something more automated and wife-friendly than this. 
> If I export the recordings directory via NFS is it
> possible to run the commercial flagging from another
> machine -- perhaps on the aforementioned front end
> which has plenty of free cycles?  Preferably just for
> this one source?  Should I turn off hyperthreading on
> the back end?  Any better ideas?
I fought a similar battle, the only difference being I was trying to 
transcode, not commflag.  From my observations, I don't believe it's a 
CPU issue:  I think it's a disk i/o issue.  I found some things that 
helped, such as adding lots more memory and enabling write-caching on 
the hard drive that holds the video (only) partition.  But I never saw 
the problem again after I set the backend to transcode only after 1:00 am.



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