Re: [PATCH 0/16 v6] PCI: Linux kernel SR-IOV support

[Avi Kivity]

Andi Kleen wrote:
> Anthony Liguori <anthony@xxxxxxxxxxxxx> writes:
>   
> > What we would rather do in KVM, is have the VFs appear in the host as
> > standard network devices.  We would then like to back our existing PV
> > driver to this VF directly bypassing the host networking stack.  A key
> > feature here is being able to fill the VF's receive queue with guest
> > memory instead of host kernel memory so that you can get zero-copy
> > receive traffic.  This will perform just as well as doing passthrough
> > (at least) and avoid all that ugliness of dealing with SR-IOV in the
> > guest.
> >     
>
> But you shift a lot of ugliness into the host network stack again.
> Not sure that is a good trade off.
>   

The net effect will be positive.  We will finally have aio networking 
from userspace (can send process memory without resorting to 
sendfile()), and we'll be able to assign a queue to a process (which 
will enable all sorts of interesting high performance things; basically 
VJ channels without kernel involvement).

> Also it would always require context switches and I believe one
> of the reasons for the PV/VF model is very low latency IO and having
> heavyweight switches to the host and back would be against that.
>   

It's true that latency would suffer (or alternatively cpu consumption 
would increase).

--
error compiling committee.c: too many arguments to function

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/