Re: [dpdk-dev] [PATCH 2/2] virtio: support IOMMU platform

[Jason Wang <jasowang@redhat.com>]

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@redhat.com 
> <mailto:mst@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.
>
>