Hi Xiao,

On 02/08/2018 03:23 AM, Wang, Xiao W wrote:
Hi Maxime,

-----Original Message-----
From: Maxime Coquelin [mailto:maxime.coque...@redhat.com]
Sent: Tuesday, February 6, 2018 10:24 PM
To: Wang, Xiao W <xiao.w.w...@intel.com>; dev@dpdk.org
Cc: Tan, Jianfeng <jianfeng....@intel.com>; Bie, Tiwei <tiwei....@intel.com>;
y...@fridaylinux.org; Liang, Cunming <cunming.li...@intel.com>; Daly, Dan
<dan.d...@intel.com>; Wang, Zhihong <zhihong.w...@intel.com>
Subject: Re: [PATCH 2/3] net/vdpa_virtio_pci: introduce vdpa sample driver

Hi Xiao,

On 02/04/2018 03:55 PM, Xiao Wang wrote:
This driver is a reference sample of making vDPA device driver based
on vhost lib, this driver uses a standard virtio-net PCI device as
vDPA device, it can serve as a backend for a virtio-net pci device
in nested VM.

The key driver ops implemented are:

* vdpa_virtio_eng_init
Mapping virtio pci device with VFIO into userspace, and read device
capability and intialize internal data.

* vdpa_virtio_eng_uninit
Release the mapped device.

* vdpa_virtio_info_query
Device capability reporting, e.g. queue number, features.

* vdpa_virtio_dev_config
With the guest virtio information provideed by vhost lib, this
function configures device and IOMMU to set up vhost datapath,
which includes: Rx/Tx vring, VFIO interrupt, kick relay.

* vdpa_virtio_dev_close
Unset the stuff that are configured previously by dev_conf.

This driver requires the virtio device supports VIRTIO_F_IOMMU_PLATFORM
, because the buffer address written in desc is IOVA.

Because vDPA driver needs to set up MSI-X vector to interrupt the guest,
only vfio-pci is supported currently.

Signed-off-by: Xiao Wang<xiao.w.w...@intel.com>
   config/common_base                                 |    6 +
   config/common_linuxapp                             |    1 +
   drivers/net/Makefile                               |    1 +
   drivers/net/vdpa_virtio_pci/Makefile               |   31 +
   .../net/vdpa_virtio_pci/rte_eth_vdpa_virtio_pci.c  | 1527
   .../rte_vdpa_virtio_pci_version.map                |    4 +
   mk/rte.app.mk                                      |    1 +
   7 files changed, 1571 insertions(+)
   create mode 100644 drivers/net/vdpa_virtio_pci/Makefile
   create mode 100644 drivers/net/vdpa_virtio_pci/rte_eth_vdpa_virtio_pci.c
   create mode 100644

Is there a specific constraint that makes you expose PCI functions and
duplicate a lot of vfio code into the driver?

The existing vfio code doesn't fit VDPA well, this vDPA driver needs to program 
IOMMU for a vDPA device with a VM's memory table.
While the eal/vfio uses a struct vfio_cfg to takes all regular devices and add 
them to a single vfio_container, and program IOMMU with DPDK process's memory 

This driver doing PCI VFIO initialization itself can avoid affecting the global 
vfio_cfg structure.

Ok, I get it.
So I think what you have to do is to extend eal/vfio for this case.
Or at least, have a vdpa layer to perform this, else every offload
driver will have to duplicate the code.

Wouldn't it be better (if possible) to use RTE_PMD_REGISTER_PCI() & co.
to benefit from all the existing infrastructure?

RTE_PMD_REGISTER_PCI() & co will make this driver as PCI driver (physical 
device), then this will conflict with the virtio_pmd.
So I make vDPA device driver as a vdev driver.

Yes, but it is a PCI device, not a virtual device. You have to extend
the EAL to support this new class of devices/drivers. Think of it as in
kernel when a NIC device can be either binded to its NIC driver, VFIO or

If I look at patch 3, you have to set --no-pci, or at least I think to
blacklist the Virtio device.

I wonder if real vDPA cards will support either vDPA mode or or behave
like a regular NIC, like the Virtio case in your example.
If this is the case, maybe the vDPA code for a NIC could be in the same
driver as the "NIC" mode.
A new struct rte_pci_driver driver flag could be introduced to specify
that the driver supports vDPA.
Then, in EAL arguments, if a vhost vdev specifies it wants Virtio device
at PCI addr 00:01:00 as offload, the PCI layer could probe this device
in "vdpa" mode.

Also, I don't know if this will be possible with real vDPA cards, but we
could have the application doing packet switching between vhost-user
vdev and the Virtio device. And at some point, at runtime, switch into
vDPA mode. This use-case would be much easier to implement if vDPA
relied on existing PCI layer.

I may be not very clear, don't hesitate to ask questions.
But generally, I think vDPA has to fit in existing DPDK architecture,
and not try to live outside of it.



Thanks for the comments,

Reply via email to