Re: [PATCH v2 1/5] dvb-core: add a new tuner ops to dvb_frontend for APIv5

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Em Sat, 06 Sep 2014 06:34:33 +0300
Antti Palosaari <crope@xxxxxx> escreveu:

> On 09/06/2014 06:17 AM, Mauro Carvalho Chehab wrote:
> > Em Sat, 06 Sep 2014 06:10:01 +0300
> > Antti Palosaari <crope@xxxxxx> escreveu:
> 
> >> ... I simply don't understand why you want hook that RF strength call
> >> via demod? The frontend cache is shared between demod and tuner. We use
> >> it for tuner driver as well demod driver. Let the tuner driver make RSSI
> >> calculation independently without any unneeded relation to demod driver.
> >
> > Well, adding kthreads has a cost, with is a way higher than just
> > calling a callback function.
> >
> > Also, it makes a way more complicated to implement several tasks.
> >
> > For example, devices with kthreads need to stop them during suspend,
> > and restart them at resume time, or otherwise suspend and/or resume
> > may not work.
> >
> > Also, the power consumption increases with kthread, as the CPU need
> > to be periodically waken.
> >
> > I'm not saying we shouldn't use kthreads at driver level, but
> > the best is to avoid when there are some other simpler ways of doing it.
> 
> And small reality check, how much you think one kthreads, that polls 
> once per 2 second or so causes, in a case when you are *already 
> streaming* 20-80 Mbit/sec data stream :) I think CPU does not need wake 
> up to execute one thread as there is a lot of other interrupts happening 
> in that use case anyway.

You can't assume that all streams received by a tuner uses 20-80Mbps. 

It could be a sound broadcasting stream, for example, with uses a much
lower bandwidth.

> We have a remote controller which is polled often as 100ms and it 
> happens even when device is "sleeping".

And lots of drivers have a modprobe parameter to disable it, because
it causes too much power consumption.

Regards,
Mauro
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