[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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