Re: [dpdk-dev] VFIO no-iommu

[Thomas Monjalon <thomas.monjalon@6wind.com>]

Hi,

2015-12-17 09:52, Burakov, Anatoly:
> > >  > > On Tue, Dec 15, 2015 at 09:53:18AM -0700, Alex Williamson wrote:
> > > > > So it works.  Is it acceptable?  Useful?  Sufficiently complete?
> > > > > Does it imply deprecating the uio interface?  I believe the
> > > > > feature that started this discussion was support for MSI/X
> > > > > interrupts so that VFs can support some kind of interrupt (uio
> > > > > only supports INTx since it doesn't allow DMA).  Implementing that
> > > > > would be the ultimate test of whether this provides dpdk with not
> > > > > only a more consistent interface, but the feature dpdk wants
> > > > > that's missing in uio. Thanks,
> > >
> > > Ferruh has done a great job so far testing Alex's patch, very few changes
> > from DPDK side seem to be required as far as existing functionality goes (not
> > sure about VF interrupts mentioned by Alex). However, one thing that
> > concerns me is usability. While it is true that no-IOMMU mode in VFIO would
> > mean uio interfaces could be deprecated in time, the no-iommu mode is way
> > more hassle than using igb_uio/uio_pci_generic because it will require a
> > kernel recompile as opposed to simply compiling and insmod'ding an out-of-
> > tree driver. So, in essence, if you don't want an IOMMU, it's becoming that
> > much harder to use DPDK. Would that be something DPDK is willing to live
> > with in the absence of uio interfaces?
> > 
> > Excuse me if I missed something obvious.
> > Why a kernel compilation is needed?
> 
> Well, not really full kernel compilation, but in the default configuration, VFIO driver would not support NOIOMMU mode. I.e. it's not compiled by default. Support for no-iommu should be enabled in kernel config and compiled in. So, whoever is going to use DPDK with VFIO-no-iommu will have to download kernel tree and recompile the VFIO module and install it. That's obviously way more hassle than simply compiling an out-of-tree driver that's already included and works with an out-of-the-box kernel.

The "out-of-the-box kernel" is configured by your distribution.
So we don't know yet what will be their choice.
If the distribution supports DPDK, it should be enabled.