Message-ID: <437C5237.3080008@drzeus.cx>
Date: Thu, 17 Nov 2005 10:49:43 +0100
From: Pierre Ossman <drzeus-list@drzeus.cx>
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To: Jens Axboe <axboe@suse.de>
CC: LKML <linux-kernel@vger.kernel.org>
Subject: Re: IOMMU and scatterlist limits
References: <437C40AE.2020309@drzeus.cx> <20051117085432.GY7787@suse.de> <437C4728.9060205@drzeus.cx> <20051117091308.GZ7787@suse.de> <437C4D14.1030101@drzeus.cx> <20051117093848.GA7787@suse.de>
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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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