[linux-dvb] Re: refactoring

[Holger Waechtler <holger@qanu.de>]

Gerd Knorr wrote:

> > > How do you check whether new data is available? Are you doing
> > > busy-polling on the write position? I wanted to wake up a
> > > poll()-waitqueue in the data-available irq, but maybe there are better
> > > ways...
> > >      
> > Well the thing is that there is almost always new data waiting (at least
> > on full-TS devices) so it's not really busy waiting. The user program just
> > gets a chunk of new packets, then does whatever it wants to them: writes
> > them to disk, sends them over the network, demultiplexes the PES for
> > decoding, etc.
> >    
> I doubt that this is true.  For example an application which does a
> channel scan wants to read just a few tables.  For 99% of the TS packets
> the "processing" is looking at the PID, noticing "oh, that one is not
> for me" and throw it away.  That will be fast enougth that the app has
> to wait for data.
>
> Even when decoding video that will be true, it takes around 10% CPU only
> on a modern desktop machine, so the app _has_ to wait at some point.  If
> it's not waiting for TS data then just because it's waiting somewhere
> else (before blitting the video frame to the screen to get the timing
> and a/v sync correct for example), not because the TS data is coming in
> fast enougth.
>  
You can wait between frames and decode then all data that is available, 
it makes no difference whether the yet-to-be decoded MPEG data is 
buffered in PES buffers inside the decoder or in the DMA ringbuffers.

Holger