From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Gunthorpe Subject: Re: [PATCH 3/5] vDPA: introduce vDPA bus Date: Mon, 20 Jan 2020 17:49:39 +0000 Message-ID: <20200120174933.GB3891@mellanox.com> References: <20200116124231.20253-1-jasowang@redhat.com> <20200116124231.20253-4-jasowang@redhat.com> <20200117070324-mutt-send-email-mst@kernel.org> <239b042c-2d9e-0eec-a1ef-b03b7e2c5419@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: Content-Language: en-US Content-ID: Sender: netdev-owner@vger.kernel.org To: Jason Wang Cc: Shahaf Shuler , Rob Miller , "Michael S. Tsirkin" , "linux-kernel@vger.kernel.org" , "kvm@vger.kernel.org" , "virtualization@lists.linux-foundation.org" , Netdev , "Bie, Tiwei" , "maxime.coquelin@redhat.com" , "Liang, Cunming" , "Wang, Zhihong" , "Wang, Xiao W" , "haotian.wang@sifive.com" , "Zhu, Lingshan" , "eperezma@redhat.com" , "lulu@redhat.com" , Parav Pandit List-Id: virtualization@lists.linuxfoundation.org On Mon, Jan 20, 2020 at 04:43:53PM +0800, Jason Wang wrote: > This is similar to the design of platform IOMMU part of vhost-vdpa. We > decide to send diffs to platform IOMMU there. If it's ok to do that in > driver, we can replace set_map with incremental API like map()/unmap(). >=20 > Then driver need to maintain rbtree itself. I think we really need to see two modes, one where there is a fixed translation without dynamic vIOMMU driven changes and one that supports vIOMMU. There are different optimization goals in the drivers for these two configurations. > > If the first one, then I think memory hotplug is a heavy flow > > regardless. Do you think the extra cycles for the tree traverse > > will be visible in any way? >=20 > I think if the driver can pause the DMA during the time for setting up ne= w > mapping, it should be fine. This is very tricky for any driver if the mapping change hits the virtio rings. :( Even a IOMMU using driver is going to have problems with that.. Jason