Re: IOMMU and scatterlist limits

[Pierre Ossman <drzeus-list@drzeus.cx>]

Jens Axboe wrote:
> On Thu, Nov 17 2005, Pierre Ossman wrote:
>   
>> Ok. Being a block device, the segments are usually rather large so the
>> overhead of setting up many DMA transfers shouldn't be that terrible.
>>     
>
> The segments will typically be paged size, so could be worse. It all
> depends on what your command overhead is like whether it hurts
> performance a lot or not.
>
>   

MMC overhead is a lot larger than sending new addr/len tuples to the 
hardware. So I suppose there is performance to be gained by iterating 
over the segments inside the driver.

Thanks for clearing things up. Maybe someone could update 
DMA-mapping.txt with the things you've explained to me here *hint* ;)

Rgds
Pierre