[dpdk-dev] [PATCH 2/2] virtio: support IOMMU platform
Jason Wang
jasowang at redhat.com
Mon Sep 5 08:31:52 CEST 2016
On 2016年09月04日 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.
>
>
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