Re: IOMMU and scatterlist limits

From: Pierre Ossman
Date: Thu Nov 17 2005 - 04:50:39 EST

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* ;)


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