On Thu, 17 Dec 2015 20:38:16 +0100
Jan Viktorin <viktorin at rehivetech.com> wrote:
> On Thu, 17 Dec 2015 11:09:23 +0100
> Thomas Monjalon <thomas.monjalon at 6wind.com> wrote:
>
> > 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.
>
> I have a question as I am not involved in all possible DPDK
> configurations, platforms, etc. and not yet very involved in vfio. What
> are the devices which do not have IOMMU? If I have, say, DPDK 2.3 with
> vfio-noiommu, which platforms (or computer systems) I am targeting?
>
> Would it be an Intel-based system? Would it be PPC8, ARM?
>
> If it is ARMv7... I would say that the fact I have to explicitly enable
> the no-IOMMU feature and rebuild the kernel (or whatever) is just OK. As
> for such systems, it is common to have a quite customized OS. Well,
> the big distributions are able to run on those devices, that's true...
> However, in such case, the users are usually skilled enough to take
> care of having their own special Linux kernel.
>
> So, is the fact the distributions would not support the no-IOMMU setup
> in their default configuration really an issue? Will some very common
> Intel/DPDK-based box need this?
>
> Regards
> Jan
So far:
* broken hardware (many systems including those from Dell) do not provide
working IOMMU because of Bios bugs etc.
* Linux guest in VMware/KVM/Hyper-V. There is no IOMMU emulation in most
of these systems.
* Older smaller systems (ie Atom) may not have IOMMU
