netdev - Re: [PATCH RFC 0/2] Packed ring for vhost

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Date:   Wed, 14 Feb 2018 04:47:34 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        wexu@...hat.com, jfreimann@...hat.com, tiwei.bie@...el.com
Subject: Re: [PATCH RFC 0/2] Packed ring for vhost

On Wed, Feb 14, 2018 at 10:37:07AM +0800, Jason Wang wrote:
> Hi all:
> 
> This RFC implement a subset of packed ring which was described at
> https://github.com/oasis-tcs/virtio-docs/blob/master/virtio-v1.1-packed-wd07.pdf
> . The code were tested with pmd implement by Jens at
> http://dpdk.org/ml/archives/dev/2018-January/089417.html. Minor
> change was needed for pmd codes to kick virtqueue since it assumes a
> busy polling backend.
> 
> Test were done between localhost and guest. Testpmd (rxonly) in guest
> reports 2.4Mpps. Testpmd (txonly) repots about 2.1Mpps.

How does this compare with the split ring design?

> It's not a complete implemention, here's what were missed:
> 
> - Device Area
> - Driver Area
> - Descriptor indirection
> - Zerocopy may not be functional
> - Migration path is not tested
> - Vhost devices except for net
> - vIOMMU can not work (mainly because the metadata prefetch is not
>   implemented).
> - See FIXME/TODO in the codes for more details
> - No batching or other optimizations were implemented

ioeventfd for PIO/mmio/s390.

> For a quick prototype, this series open code the tracking of warp
> counter and descriptor index at net device. This will be addressed in
> the future by:
> 
> - Move get_rx_bufs() from net.c to vhost.c
> - Let vhost_get_vq_desc() returns vring_used_elem instad of head id
> 
> With the above, we can hide the internal (at least part of) vring
> layout from specific device.
> 
> Please review.
> 
> Thanks
> 
> Jason Wang (2):
>   virtio: introduce packed ring defines
>   vhost: packed ring support
> 
>  drivers/vhost/net.c                |  14 +-
>  drivers/vhost/vhost.c              | 351 ++++++++++++++++++++++++++++++++++---
>  drivers/vhost/vhost.h              |   6 +-
>  include/uapi/linux/virtio_config.h |   9 +
>  include/uapi/linux/virtio_ring.h   |  17 ++
>  5 files changed, 369 insertions(+), 28 deletions(-)
> 
> -- 
> 2.7.4