[dpdk-dev] [Question] How pmd virtio works without UIO?

[Yuanhan Liu]

On Wed, Dec 23, 2015 at 10:41:57AM +0800, Peter Xu wrote:
> On Wed, Dec 23, 2015 at 10:01:35AM +0800, Yuanhan Liu wrote:
> > On Tue, Dec 22, 2015 at 05:56:41PM +0800, Peter Xu wrote:
> > > On Tue, Dec 22, 2015 at 04:32:46PM +0800, Yuanhan Liu wrote:
> > > > Actually, you are right. I mentioned in the last email that this is
> > > > for configuration part. To answer your question in this email, you
> > > > will not be able to go that further (say initiating virtio pmd) if
> > > > you don't unbind the origin virtio-net driver, and bind it to igb_uio
> > > > (or something similar).
> > > > 
> > > > The start point is from rte_eal_pci_scan, where the sub-function
> > > > pci_san_one just initates a DPDK bond driver.
> > > 
> > > I am not sure whether I do understand your meaning correctly
> > > (regarding "you willl not be able to go that furture"): The problem
> > > is that, we _can_ run testpmd without unbinding the ports and bind
> > > to UIO or something. What we need to do is boot the guest, reserve
> > > huge pages, and run testpmd (keeping its kernel driver as
> > > "virtio-pci"). In pci_scan_one():
> > > 
> > > 	if (!ret) {
> > > 		if (!strcmp(driver, "vfio-pci"))
> > > 			dev->kdrv = RTE_KDRV_VFIO;
> > > 		else if (!strcmp(driver, "igb_uio"))
> > > 			dev->kdrv = RTE_KDRV_IGB_UIO;
> > > 		else if (!strcmp(driver, "uio_pci_generic"))
> > > 			dev->kdrv = RTE_KDRV_UIO_GENERIC;
> > > 		else
> > > 			dev->kdrv = RTE_KDRV_UNKNOWN;
> > > 	} else
> > > 		dev->kdrv = RTE_KDRV_UNKNOWN;
> > > 
> > > I think it should be going to RTE_KDRV_UNKNOWN
> > > (driver=="virtio-pci") here.
> > 
> > Sorry, I simply overlook that. I was thinking it will quit here for
> > the RTE_KDRV_UNKNOWN case.
> > 
> > > I tried to run IO and it could work,
> > > but I am not sure whether it is safe, and how.
> > 
> > I also did a quick test then, however, with the virtio 1.0 patchset
> > I sent before, which sets the RTE_PCI_DRV_NEED_MAPPING, resulting to
> > pci_map_device() failure and virtio pmd is not initiated at all.
> 
> Then, will the patch work with ioport way to access virtio devices?

Yes.

> 
> > 
> > > 
> > > Also, I am not sure whether I need to (at least) unbind the
> > > virtio-pci driver, so that there should have no kernel driver
> > > running for the virtio device before DPDK using it.
> > 
> > Why not? That's what the DPDK document asked to do
> > (http://dpdk.org/doc/guides/linux_gsg/build_dpdk.html):
> > 
> >     3.6. Binding and Unbinding Network Ports to/from the Kernel Modules
> >     
> >     As of release 1.4, DPDK applications no longer automatically unbind
> >     all supported network ports from the kernel driver in use. Instead,
> >     all ports that are to be used by an DPDK application must be bound
> >     to the uio_pci_generic, igb_uio or vfio-pci module before the
> >     application is run. Any network ports under Linux* control will be
> >     ignored by the DPDK poll-mode drivers and cannot be used by the
> >     application.
> 
> This seems obsolete? since it's not covering ioport.

I don't think so. Above is for how to run DPDK applications. ioport
is just a (optional) way to access PCI resource in a specific PMD.

And, above speicification avoids your concerns, that two drivers try
to manipulate same device concurrently, doesn't it?

And, it is saying "any network ports under Linux* control will be
ignored by the DPDK poll-mode drivers and cannot be used by the
application", so that the case you were saying that virtio pmd
continues to work without the bind looks like a bug to me.

Can anyone confirm that?

	--yliu