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DateThu, 17 Nov 2005 10:49:43 +0100
FromPierre Ossman <>
SubjectRe: IOMMU and scatterlist limits
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

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