[linux-dvb] Re: Reading from 4 cards simultaneously?

[Jon Burgess]

I have 4 budget Nova-T PCI cards in my PC and it works OK. This is with 
a reasonably spec'd normal desktop motherboard with a Intel 865G chipset 
with a single standard 32bit/33MHz PCI bus (Gigabyte GA-8IG1000 Pro).

You could try changing the DMA burst settings. I believe the default 
settings result in a poor PCI bus utilisation, perhaps this combined 
with the extra latency introduced by the PCI bridge causes the problems. 
The DMA burst settings were discussed some time ago on this list -

This email provided a patch to make the DMA bursting tweakable module 
parameter
http://www.linuxtv.org/mailinglists/linux-dvb/2003/08-2003/msg00462.html

The comments in the patch describing the register values were not quite 
right, see this followup for details
http://www.linuxtv.org/mailinglists/linux-dvb/2003/09-2003/msg00004.html

I believe that you should try increasing the burst size to 16 DWords. 
This matches the cacheline size of the P4 CPU which should improve 
things. Unfortunately I don't think the PCI card supports the cacheline 
write (MWI), it looks like the Philips chip was designed without reading 
the Intel guidelines on how to support efficient DMA transfers on a PCI bus.

   Jon



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