From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: Re: [PATCH 2/2] virtio: support IOMMU platform Date: Mon, 5 Sep 2016 14:31:52 +0800 Message-ID: References: <1472798220-7121-1-git-send-email-jasowang@redhat.com> <1472798220-7121-2-git-send-email-jasowang@redhat.com> <1631660.hGMgJuvotI@xps13> <20160902202613-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Cc: Thomas Monjalon , dev , huawei.xie@intel.com, yuanhan.liu@linux.intel.com To: Alejandro Lucero , "Michael S. Tsirkin" Return-path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by dpdk.org (Postfix) with ESMTP id B93B25595 for ; Mon, 5 Sep 2016 08:31:58 +0200 (CEST) In-Reply-To: List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" 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 > 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. > >