[mythtv] Mythbackend: Large ni CPU usage when idle ?

Nigel Pearson nigel at ind.tansu.com.au
Mon Nov 1 23:55:41 UTC 2004

	These really are questions for the users list, but...

> Generally all is working fine. However I have noticed that after 
> viewing
> some recordings the mythbackend box is showing the CPU nice usage to
> be about 56% using "top".

	That happens to me when I forget to turn DMA on for the
drive that holds my recordings, but high network usage can also
do it. I assume that the usage drops to nearly 0 after a while?

	Have you run any verseion other than CVS?
(i.e. has the behaviour changed?)

>  The "top" process listing does not show any particular process using 
> the CPU in the %CPU column.

	Look at the lines up the top, the Cpu(s) one.
Is any one of those particularly high? Maybe sy? (System)
That may indicate lots of IO that the kernel is doing.
Note that different versions of top have different field names.

>  If I kill and restart mythbackend nice usage goes down to 0 again 
> until I watch another recording.
> Any ideas on:
> 1. Why is mythbackend using the CPU with nice priority when idle ?

	That is a good thing! Positive nice values mean that other tasks
(like the frontend, or mplayer for watching a DVD) get a little bit
more CPU time.

> 2. Why does "top" not show mythbackend using the CPU in %CPU ?

	Probably because the backend is doing very little.
DVB cards provide pre-compressed data, so all the backend
does is initiate the tuner, supervise the PCI buss transfers,
and write a little bit of data into a file or network socket.
A very efficient setup.

Nigel Pearson, nigel at ind.tansu.com.au | "Reality is that which,
Telstra BI&D, Sydney, Australia       |  when you stop believing
Office: 8255 4222    Fax:  8255 3153  |  in it, doesn't go away."
Mobile: 0408 664435  Home: 9792 6998  |  Philip K. Dick - 'Valis'

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