On 2016?09?04? 16:08, Alejandro Lucero wrote: > 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.
We will use qemu vIOMMU for virito, so there's no such issue. > I'm talking about IOMMU contention, exactly about IOTLB contention. I thought device IOTLB (ATS) was just designed to solve this 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? For virtio, we use vIOMMU per VM and implement a device IOTLB in vhost side. Technically, it does not have such issue I think. Thanks > > On Fri, Sep 2, 2016 at 6:26 PM, Michael S. Tsirkin <mst at redhat.com > <mailto: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. > >
