Hi Damjan, My understanding is that CONFIG_VFIO_NOIOMMU will never be set in a stock kernel, and you will need to build a custom kernel for that. I understand that with this option, the kernel cannot guarantee that applications are prevented from creating bugs that normally the kernel can guarantee will not occur (outside of a kernel bug.) It therefore violates the fundamental Linux system design. That being said, you may wish to accept the risk for performance reasons and build a custom kernel. The other strange thing would be that MSI or MSI-X style interrupts are not needed for performance. The people who developed them have made a lot of noise about how they came about for performance reasons. I have no direct experience, but to learn that they are not important is a shock.
It seems to me that the Ubuntu 14.04 issue is really a separate one from all of this, although I would imagine that the conclusion to stop supporting it does not change. Burt On Tue, Jan 24, 2017 at 1:07 PM, Damjan Marion (damarion) < damar...@cisco.com> wrote: > > > On 24 Jan 2017, at 18:40, Damjan Marion (damarion) <damar...@cisco.com> > wrote: > > > >> > >> On 24 Jan 2017, at 18:26, Stephen Hemminger <step...@networkplumber.org> > wrote: > >> > >> On Tue, 24 Jan 2017 17:14:42 +0000 > >> "Damjan Marion (damarion)" <damar...@cisco.com> wrote: > >> > >>> Is anybody aware of any valid reason why we cannot switch to > uio_pci_generic > >>> as default PCI uio driver in ubuntu packages? > >>> > >>> I think generally people don’t like out-of-tree modules, so as long as > we are getting > >>> the same service from uio_pci_generic we should use it… > >>> > >>> Thanks, > >>> > >>> Damjan > > > >> uio_pci_generic does not support MSI or MSI-X interrupts, only legacy > INTX. > > > > I know but do we really care? > > > >> > >> The preference should always be to use VFIO. Even on systems without > IOMMU. > > > > What is the perf impact? > > > > Also, I just tried with kernel 4.8 on rangeley ATOM, and i got: > > > > [536030.250072] vfio-pci: probe of 0000:00:14.0 failed with error -22 > > [536030.253271] vfio-pci: probe of 0000:00:14.0 failed with error -22 > > > > I guess I’m doing something wrong…. > > This explains: > > grep VFIO_NOIO /boot/config-4.8.0-34-generic > # CONFIG_VFIO_NOIOMMU is not set > > So vfio is out of the game of being default choice, people can still > switch simply with one line change in /etc/vpp/startup.conf. > > > _______________________________________________ > vpp-dev mailing list > vpp-dev@lists.fd.io > https://lists.fd.io/mailman/listinfo/vpp-dev >
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