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Date: Sun, 20 Apr 2008 14:29:43 -0500
From: Anthony Liguori <aliguori@us.ibm.com>
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Subject: Re: [kvm-devel] [Qemu-devel] [PATCH 1/5] PCI DMA API (v3)
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To: Blue Swirl <blauwirbel@gmail.com>
Cc: kvm-devel@lists.sourceforge.net, Marcelo Tosatti <marcelo@kvack.org>, qemu-devel@nongnu.org, Aurelien Jarno <aurelien@aurel32.net>, Paul Brook <paul@codesourcery.com>

Blue Swirl wrote:
> On 4/19/08, Anthony Liguori <anthony@codemonkey.ws> wrote:
>   
> Well, the IOVector part and bdrv_readv look OK, except for the heavy
> mallocing involved.
>   

I don't think that in practice, malloc is going to have any sort of 
performance impact.  If it does, it's easy enough to implement a small 
object allocator for common, small vector sizes.

> I'm not so sure about the DMA side and how everything fits together
> for zero-copy IO. For example, do we still need explicit translation
> at some point?

I'm thinking that zero copy will be implemented by setting the map and 
unmap functions to NULL by default (instead of to the PCI read/write 
functions).  Then the bus can decide whether copy functions are needed.  
I'll send an updated patch series tomorrow that includes this functionality.

Regards,

Anthony Liguori