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

[Holger Waechtler <holger@qanu.de>]

Juergen Pfennig wrote:

> 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?
you can do so if you want, that's the intention of this ioctl(). But is 
it really needed? Our experiences showed that these values are usually 
ok for normal environments.

Holger