On Mon, Jun 27, 2011 at 12:02 PM, Russell King - ARM Linux
[off-list ref] wrote:

The next thing to think about in DMA-land is whether we should total up
the size of the SG list and choose whether to flush the individual SG
elements or do a full cache flush. ?There becomes a point where the full
cache flush becomes cheaper than flushing each SG element individually.

We noticed that even for a single (large) buffer, any cache flush operation
above a certain threshold flushing indiviudal lines become more expensive
than flushing the entire cache.

I requested colleagues to look into implenting this threshold in the
arch/arm/mm/cache-v7.S file. but I think they ran into trouble and
eventually had to give up on it.

Vijay or Srinidhi, can you share your findings?

Thanks,
Linus Walleij