Re: [kvm-devel] [Qemu-devel] [PATCH 1/5] PCI DMA API (v3)

[Anthony L. <ali...@us...>]

Blue Swirl wrote:
> On 4/19/08, Anthony Liguori <an...@co...> 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