On Tue, 24 Jan 2017 23:05:55 -0500 Burt Silverman <bur...@gmail.com> wrote:
> 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 > The reality is any userspace I/O without IOMMU is insecure and can introduce bugs. It was only when changes to UIO were proposed that the UIO maintainer realized the problem and would not accept changes. The VFIO maintainer was more enlightened "if you want to hang yourself, and you sign the disclaimer, here is a prettier rope". MSI-X allows DPDK applications to be built with a hybrid polling model which is better for power and CPU consumption. Unfortunately this is supportable only on some drivers, and configurations; plus from my terse reading of the FD.IO code it is not possible now. Pure polling is a great only if you don't have to ever pay for power or CPU cycles. It sucks in virtual environments. _______________________________________________ vpp-dev mailing list vpp-dev@lists.fd.io https://lists.fd.io/mailman/listinfo/vpp-dev
