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

[Oliver Endriss <o.endriss@gmx.de>]

On Monday 14 July 2003 14:48, Johannes Stezenbach wrote:
> 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.

According to oprofile the load is caused by the busy-waiting stuff in 
the i2c code. The zig-zag scan isn't a problem, because the fe thread 
*sleeps* for 200ms after each tuning attempt.

BTW, I had a look into dvb-kernel and noticed that the i2c code is 
interrupt-driven. A quick test showed that the fe thread caused 
virtually no cpu load, even if the sat signal is missing!

Maybe the guys who use the DVB-S without a dish should simply switch to 
dvb-kernel...

Oliver


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