I know RedHat is working on a vIOMMU so I guess this work is related to that effort, but it is a surprise virtio using IOMMU. I thought IOMMU just made sense when using SRIOV. My second guess is using IOMMU with virtio is a matter of security, but by other hand, virtio + IOMMU could imply serious performance degradation when multiple VMs are in use. I'm talking about IOMMU contention, exactly about IOTLB contention. This performance issue is complex to describe or even analyze as there are several factors having an impact on it. For example, 1GB hugepages can avoid most of it and the same if TX & RX rings are not bigger than 256. So, my question: is RedHat aware of this potential IOMMU contention which can limit scalability?
On Fri, Sep 2, 2016 at 6:26 PM, Michael S. Tsirkin <mst at redhat.com> wrote: > On Fri, Sep 02, 2016 at 03:04:56PM +0200, Thomas Monjalon wrote: > > 2016-09-02 14:37, Jason Wang: > > > Virtio pmd doesn't support VFIO in the past since devices bypass IOMMU > > > completely. But recently, the work of making virtio device work with > > > IOMMU is near to complete. > > > > Good news! > > What are the requirements for Qemu and Linux version numbers please? > > I expect QEMU 2.8 and Linux 4.8 to have the support. >
