[mythtv-users] LiveTV without the disk buffering

Håkon Alstadheim hakon at alstadheim.priv.no
Tue Jan 8 19:58:49 UTC 2008

About mythfrontend using too much cpu
[various suggestions for reducing cpu-intensity of mythfrontend snipped ...]

I'm also experiencing the same kinds of problems. FE takes 40-60% cpu, 
BE 50-70% cpu. Both together == stuttering playback. Mine started after 
an upgrade from 0.20.x to 0.21 svn. The problems have been worse when 
the recorded file had lots of bits per second (due to noisy signal or 
bad encoding ), so I also suspected the hard-drive at first. However, 
running vlc for playback while recording with mythbackend gives mostly 
smooth runnings, so I've been looking at other possible culprits. I 
THINK I've seen some improvements lately when I've tried to tune the 
mysql buffer sizes, even though mysql never shows up in top. Is the 
cpu-usage for mysql-threads counted towards the client process ? I also 
suspect the stuttering happens more often when my network drops out. 
Even though my box is a combined fe/be, I'm wondering whether the fact 
that my network switch has a tendency to reboot spontaneously (don't 
ask) might be a factor here, especially since the myth storage is on a 
usb device. Migtht a network dropout cause delays in the kernel 
processing of usb disk IO? Anyway, hdparm shows ~26MB/sec buffered disk 
reads to the mythtv storage device, which should be sufficient. (yes 
mysql storage is on a different device).

One notable quirk about my setup is that although I run a combined 
FE/BE, I run with different users for FE and BE. Might this be a 
contributing factor?

Any suggestions for stuff to try would be appreciated. I've looked at 
everything I could think of. iostat, top, /var/log/*, system info in 
phpmyadmin . Problem is I don't know what I'm looking for.

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