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SubjectRe: [PATCH 0/16 v6] PCI: Linux kernel SR-IOV support
Andi Kleen wrote:
> Anthony Liguori <anthony@codemonkey.ws> 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



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