[linux-dvb] DVB cards in a Server, Buffer sizes

[Juergen Pfennig <info@j-pfennig.de>]

Hi Dear DVB Developers,
your drivers appear now to be stable enough to be run in a server computer. 
This makes sense if you want to burden that poor PC with cron or atd based 
batch recording of TV or Radio programs (see my zapdvb project). Now my 
little question (code below derived from szap.c) :

bool ZTuning::setDemux(HANDLE dmxfd, bool bAudio, bool bDvr)
{
 if(bDvr) {
  int buffersize = 64 * 1024;
  if (ioctl(dmxfd, DMX_SET_BUFFER_SIZE, buffersize) == -1) {
   ZZapDvb::printError("DVB setup (ioctl DMX_SET_BUFFER_SIZE) failed:");
   return false;
  }
 }
 ....bla bla bla...
}

As you can see the s/t/c-zap family of programs sets a buffer size of 64kByte 
on the demux device. This is not very much. Even a workstation can be 
(disk-io) busy for a few seconds - not to mention a server. I do not want to 
discuss the problem of missing (disk-)io priorities in the kernel, but my 
question simply is:

    IS IT RECOMMENDED AND SAFE TO USE A LARGER BUFFER?

I would feel better to tell the driver to grab 512 kByte of precious kernel 
memory. What do you think?

Yours Jürgen