[PATCH v6 00/11] mmc: use nonblock mmc requests to minimize latency

[Russell King - ARM Linux]

On Mon, Jun 27, 2011 at 11:42:52AM +0200, Per Forlin wrote:
> Conclusion:
> Working with mmc the relative cost of DSB is almost none. There seems
> to be slightly higher number for mmc blocking requests with the DSB
> patch compared to not having it.

These figures suggest that dsb is comparitively not heavy on the hardware
you're testing.

I think I'm going to apply the patch anyway - it certainly makes stuff
no worse, and if someone has a platform where dsb is more expensive,
then they should see a greater benefit from this change.

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.