Re: [RFC] [PATCH 0/3] ioat: DMA engine support

[Avi Kivity]

Andi Kleen wrote:

> > >      
> > As an example, an NFS server reads some data pages using iSCSI and sends 
> > them using NFS/TCP (or vice versa).
> >    
>
> For TX this can be done zero copy using a sendfile like setup.
>  
Yes, or with aio send for anonymous memory.

> For RX it may help - but my point was that most applications
> are not structured in this simple way.
>
>  
Agreed. But those that do care, care very much. The data mover 
applications, simply because they don't touch the data, expect very high 
bandwidth.

> > As long as they can be turned off. Not all usespace applications want to 
> > touch the data immediately.
> >    
>
> Perhaps.  And lots of others might. Of course the simple
> network benchmarks don't so the number on them look good.
>
>  
There are very real non-benchmark applications that want this.

> Just pointing out that it's not clear it will always be a big help.
>
>  
Agree it should default to in-cache.

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