[Cbe-oss-dev] Spider DMA wrongness

Linas Vepstas linas at austin.ibm.com
Fri Dec 15 07:21:12 EST 2006

On Tue, Nov 07, 2006 at 04:43:07PM +1100, Benjamin Herrenschmidt wrote:
>  - The descriptor ring mixes up descriptors themselves and driver
> specific data. This is pretty bad. That means bad cache behaviour and
> the descriptors as seen by the hardware aren't nicely next to each other
> in memory, thus defeating any possible attempt at prefetching the chip
> might be doing (most network chips do aggressive prefetching of
> descriptors, I don't know for sure about spider). We should really
> really really (I insist :-) split the actual descriptors manipulated by
> the driver and the device (DMA) from the driver data structures. The

Guhh. I just unearthed this old, unread chain of notes.  I'll try
sending a patch shortly.


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