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From: Jason Gunthorpe <jgg@nvidia.com>
To: Thomas Monjalon <thomas@monjalon.net>
Cc: "Xia, Chenbo" <chenbo.xia@intel.com>,
	"dev@dpdk.org" <dev@dpdk.org>,
	"Liang, Cunming" <cunming.liang@intel.com>,
	"Wu, Jingjing" <jingjing.wu@intel.com>,
	"Burakov, Anatoly" <anatoly.burakov@intel.com>,
	"Yigit, Ferruh" <ferruh.yigit@intel.com>,
	"mdr@ashroe.eu" <mdr@ashroe.eu>,
	"nhorman@tuxdriver.com" <nhorman@tuxdriver.com>,
	"Richardson, Bruce" <bruce.richardson@intel.com>,
	"david.marchand@redhat.com" <david.marchand@redhat.com>,
	"stephen@networkplumber.org" <stephen@networkplumber.org>,
	"Ananyev, Konstantin" <konstantin.ananyev@intel.com>,
	parav@nvidia.com, xuemingl@nvidia.com
Subject: Re: [dpdk-dev] [RFC v3 0/6] Add mdev (Mediated device) support in DPDK
Date: Tue, 15 Jun 2021 08:57:27 -0300
Message-ID: <20210615115727.GQ1002214@nvidia.com> (raw)
In-Reply-To: <50744230.0ZSezZt4d8@thomas>

On Tue, Jun 15, 2021 at 09:48:24AM +0200, Thomas Monjalon wrote:
> 15/06/2021 04:49, Xia, Chenbo:
> > From: Thomas Monjalon <thomas@monjalon.net>
> > > 01/06/2021 05:06, Chenbo Xia:
> > > > Hi everyone,
> > > >
> > > > This is a draft implementation of the mdev (Mediated device [1])
> > > > support in DPDK PCI bus driver. Mdev is a way to virtualize devices
> > > > in Linux kernel. Based on the device-api (mdev_type/device_api),
> > > > there could be different types of mdev devices (e.g. vfio-pci).
> > > 
> > > Please could you illustrate with an usage of mdev in DPDK?
> > > What does it enable which is not possible today?
> > 
> > The main purpose is for DPDK to drive mdev-based devices, which is not
> > possible today.
> > 
> > I'd take PCI devices for an example. Currently DPDK can only drive devices
> > of physical pci bus under /sys/bus/pci and kernel exposes the pci devices
> > to APP in that way.
> > 
> > But there are PCI devices using vfio-mdev as a software framework to expose
> > Mdev to APP under /sys/bus/mdev. Devices could choose this way of virtualizing
> > itself to let multiple APPs share one physical device. For example, Intel
> > Scalable IOV technology is known to use vfio-mdev as SW framework for Scalable
> > IOV enabled devices (and Intel net/crypto/raw devices support this tech). For
> > those mdev-based devices, DPDK needs support on the bus layer to scan/plug/probe/..
> > them, which is the main effort this patchset does. There are also other devices
> > using the vfio-mdev framework, AFAIK, Nvidia's GPU is the first one using mdev
> > and Intel's GPU virtualization also uses it.
> 
> Yes mdev was designed for virtualization I think.
> The use of mdev for Scalable IOV without virtualization
> may be seen as an abuse by Linux maintainers,
> as they currently seem to prefer the auxiliary bus (which is a real bus).
> 
> Mellanox got a push back when trying to use mdev for the same purpose
> (Scalable Function, also called Sub-Function) in the kernel.
> The Linux community decided to use the auxiliary bus.
> 
> Any other feedback on the choice mdev vs aux?
> Is there any kernel code supporting this mdev model for Intel devices?

IMHO until a kernel networking driver is accepted that uses mdev this
is all just dead code in dpdk and shouldn't be merged.

I think it is unlikely that future networking drivers will use mdev.

> > > > 2: A new mdev bus that scans mediated pci devices and probes mdev driver to
> > > >    plug-in pci devices to pci bus

And we are likely not doing 'mediated pci devices' at all..

Jason

      parent reply	other threads:[~2021-06-16  6:08 UTC|newest]

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-03  7:18 [dpdk-dev] [RFC 0/3] " Tiwei Bie
2019-04-03  7:18 ` Tiwei Bie
2019-04-03  7:18 ` [dpdk-dev] [RFC 1/3] eal: add a helper for reading string from sysfs Tiwei Bie
2019-04-03  7:18   ` Tiwei Bie
2019-04-03  7:18 ` [dpdk-dev] [RFC 2/3] bus/mdev: add mdev bus support Tiwei Bie
2019-04-03  7:18   ` Tiwei Bie
2019-04-03  7:18 ` [dpdk-dev] [RFC 3/3] bus/pci: add mdev support Tiwei Bie
2019-04-03  7:18   ` Tiwei Bie
2019-04-03 14:13   ` Wiles, Keith
2019-04-03 14:13     ` Wiles, Keith
2019-04-04  4:19     ` Tiwei Bie
2019-04-04  4:19       ` Tiwei Bie
2019-04-08  8:44 ` [dpdk-dev] [RFC 0/3] Add mdev (Mediated device) support in DPDK Alejandro Lucero
2019-04-08  8:44   ` Alejandro Lucero
2019-04-08  9:36   ` Tiwei Bie
2019-04-08  9:36     ` Tiwei Bie
2019-04-10 10:02     ` Francois Ozog
2019-04-10 10:02       ` Francois Ozog
2019-07-15  7:52 ` [dpdk-dev] [RFC v2 0/5] " Tiwei Bie
2019-07-15  7:52   ` [dpdk-dev] [RFC v2 1/5] bus/pci: introduce an internal representation of PCI device Tiwei Bie
2019-07-15  7:52   ` [dpdk-dev] [RFC v2 2/5] bus/pci: avoid depending on private value in kernel source Tiwei Bie
2019-07-15  7:52   ` [dpdk-dev] [RFC v2 3/5] bus/pci: introduce helper for MMIO read and write Tiwei Bie
2019-07-15  7:52   ` [dpdk-dev] [RFC v2 4/5] eal: add a helper for reading string from sysfs Tiwei Bie
2019-07-15  7:52   ` [dpdk-dev] [RFC v2 5/5] bus/pci: add mdev support Tiwei Bie
2021-06-01  3:06     ` [dpdk-dev] [RFC v3 0/6] Add mdev (Mediated device) support in DPDK Chenbo Xia
2021-06-01  3:06       ` [dpdk-dev] [RFC v3 1/6] bus/pci: introduce an internal representation of PCI device Chenbo Xia
2021-06-01  3:06       ` [dpdk-dev] [RFC v3 2/6] bus/pci: avoid depending on private value in kernel source Chenbo Xia
2021-06-01  3:06       ` [dpdk-dev] [RFC v3 3/6] bus/pci: introduce helper for MMIO read and write Chenbo Xia
2021-06-01  3:06       ` [dpdk-dev] [RFC v3 4/6] eal: add a helper for reading string from sysfs Chenbo Xia
2021-06-01  5:37         ` Stephen Hemminger
2021-06-08  5:47           ` Xia, Chenbo
2021-06-01  5:39         ` Stephen Hemminger
2021-06-08  5:48           ` Xia, Chenbo
2021-06-11  7:19         ` Thomas Monjalon
2021-06-01  3:06       ` [dpdk-dev] [RFC v3 5/6] bus/pci: add mdev support Chenbo Xia
2021-06-01  3:06       ` [dpdk-dev] [RFC v3 6/6] bus/pci: add sparse mmap support for mediated PCI devices Chenbo Xia
2021-06-11  7:15       ` [dpdk-dev] [RFC v3 0/6] Add mdev (Mediated device) support in DPDK Thomas Monjalon
2021-06-15  2:49         ` Xia, Chenbo
2021-06-15  7:48           ` Thomas Monjalon
2021-06-15 10:44             ` Xia, Chenbo
2021-06-15 11:57             ` Jason Gunthorpe [this message]

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