[linux-dvb] Re: full featured card without signal and required video memory investigation

[Johannes Stezenbach <js@convergence.de>]

Oliver Endriss wrote:
> On Friday 11 July 2003 12:10, Oliver Endriss wrote:
> >
> > I simply removed the sat cable from the box. Then the [kdvb-fe-0:0]
> > frontend process consumes approx. 30% cpu while it tries to retune.
> > AFAIK this is normal behaviour.
> >
> > Then I played some recordings. Nothing happened.
> 
> Second test completed successfully. My system was running more than 15 
> hours without sat signal. No problems. The frontend process consumed 
> 30-35% CPU power. I'll check what causes this high load as soon as I 
> get oprofile running on my machine. ;-)

There are two things that cause the high load:
- the I2C driver
- the frontend thread that uses I2C to talk to the frontend

If you can improve the I2C driver, great. But the load won't go unless
we change the frontend thread. Which isn't difficult, but it is a
policy decision.

Holger defined the current policy as "if tuning fails, do an endless
zig-zag scan as an attempt to recover a signal". Since a STB is quite
useless if you have no signal, and the frontend thread runs with idle
priority, this makes some sense. If you unplug your antenna, and then
replug it, your signal is quickly back.

On a PC things are a little different. A more suitable policy would
be, e.g. "if tuning fails, try one zig-zag scan, and if that doesn't
work just probe on the given frequency once a second". Or use a module
parameter to disable this recovery completely.

A final note: If no program has the frontend opened, and the module
parameter dvb_shutdown_timeout is != 0 (5 is default), the frontend
thread exits and the frontend is powered down.

Johannes


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