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

[Per Forlin]

On 27 June 2011 12:02, Russell King - ARM Linux <linux at arm.linux.org.uk> wrote:
> 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.
>
Yes, of course.

> 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.
>
I agree.

> 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.
>
Interesting.
I have seen such optimisations in hwmem (yet another memory manager
for multi media hardware). It would be nice to have such functionality
in dma-mapping, to be used by anyone

Regards,
Per