[mythtv-users] Fedora help needed: Hard disk access is sometimes slow (DMA is on)

[Thomas Börkel]

HI!

My Myth box worked like a charm from february until about 3 weeks ago.

Now I get occasionally stuttering video during playback (mythfrontend 
says "prebuffering pause". I also have some strange entries from 
mythbackend (IOBOUND - blocking in ThreadedFileWriter::Write()) and the 
scheduler today took 19 seconds to schedule where it normally takes 0.5 
seconds.

These effects are not all the time. They come and go. When it happens, 
the HD LED blinks very bright (= quick) during accesses.

For example, during playback, it normally blinks only with short 
flashes. But when it happens, it looks like multiple threads would 
access the HD. When I press pause, blinking stopps completely, so there 
is no other process accessing. Resuming playback results in heavy 
blinking again. This lasts for a minute or two, then it's back to normal 
again.

Sometimes, starting mythfrontend is quick as usual, sometimes it takes long.

hdparm tells that DMA is on (udma4) and that it's fast (60 MB/s with -t).

top tells that there is nothing unusual going on and there is very 
little swap space used.

I also found nothing unusual in dmesg or /var/log/messages.

There are no interrupt errors in /proc/interrupts.

I am not aware that I changed anything that could be related.

May-be related info:
- one box for frontend and backend (installed using Jarod's guide)
- root filesystem is ext3
- filesystem for recordings partition is XFS
- using NVidia (4363) TV-out with XV
- commercial flagging is OFF

System:
- Myth 0.15.1
- Fecora Core 1
- Kernel 2.4, 2197
- ivtv 0.1.10pre2 ck36c
- 512 MB RAM, Celeron 2.6 GHz

Anyone any hints?

Thanks!

Thomas