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Re: [RFC 0/2] Virtio in order feature support for virtio-net device.


From: Jason Wang
Subject: Re: [RFC 0/2] Virtio in order feature support for virtio-net device.
Date: Thu, 25 Aug 2022 14:08:27 +0800

On Thu, Aug 18, 2022 at 11:13 PM Guo Zhi <qtxuning1999@sjtu.edu.cn> wrote:
>
> In virtio-spec 1.1, new feature bit VIRTIO_F_IN_ORDER was introduced.
> When this feature has been negotiated, virtio driver will use
> descriptors in ring order: starting from offset 0 in the table, and
> wrapping around at the end of the table. Virtio devices will always use
> descriptors in the same order in which they have been made available.
> This can reduce virtio accesses to used ring.

So the bached used buffer seems like an optimization, I'd like
re-order the patches

1) Just enable virtio-net in-order without the batching, to see the performance
2) Add the batching optimization on top.

>
> Based on updated virtio-spec, this series realized IN_ORDER prototype
> for virtio-net device in QEMU.

Please share with us some performance numbers. E.g pps.

>
> Some work haven't been done in this patch series:
> 1. Virtio device in_order support for packed vq is left for the future.

Anything makes packed virtqueue special?

Thanks

>
> Related patches:
> In order feature in Linux(support virtio driver, vhost_test and vsock 
> device): https://lkml.org/lkml/2022/8/17/643
>
> Guo Zhi (2):
>   virtio: expose used buffers
>   virtio: enable f_in_order feature for virtio-net
>
>  hw/net/virtio-net.c        | 30 +++++++++++++++++++++++++++---
>  include/hw/virtio/virtio.h |  4 +++-
>  2 files changed, 30 insertions(+), 4 deletions(-)
>
> --
> 2.17.1
>




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