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[79.176.41.183]) by smtp.gmail.com with ESMTPSA id d206sm3549894qke.66.2020.02.12.01.55.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 12 Feb 2020 01:55:42 -0800 (PST) Date: Wed, 12 Feb 2020 04:55:38 -0500 From: "Michael S. Tsirkin" To: Jason Wang Subject: Re: [PATCH v2 1/5] virtio-mmio: add notify feature for per-queue Message-ID: <20200212045245-mutt-send-email-mst@kernel.org> References: <8a4ea95d6d77a2814aaf6897b5517353289a098e.1581305609.git.zhabin@linux.alibaba.com> <20200211062205-mutt-send-email-mst@kernel.org> <20200212024158-mutt-send-email-mst@kernel.org> <82d99b35-0c64-2eb2-9c23-7af2597b880b@redhat.com> MIME-Version: 1.0 In-Reply-To: <82d99b35-0c64-2eb2-9c23-7af2597b880b@redhat.com> X-MC-Unique: 8XMyXpizNdCE1PuNpOOa3A-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: virtio-dev@lists.oasis-open.org, Zha Bin , slp@redhat.com, jing2.liu@linux.intel.com, linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, chao.p.peng@linux.intel.com, gerry@linux.alibaba.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Feb 12, 2020 at 05:33:06PM +0800, Jason Wang wrote: >=20 > On 2020/2/12 =E4=B8=8B=E5=8D=884:53, Jason Wang wrote: > >=20 > > On 2020/2/12 =E4=B8=8B=E5=8D=884:18, Michael S. Tsirkin wrote: > > > On Wed, Feb 12, 2020 at 11:39:54AM +0800, Jason Wang wrote: > > > > On 2020/2/11 =E4=B8=8B=E5=8D=887:33, Michael S. Tsirkin wrote: > > > > > On Mon, Feb 10, 2020 at 05:05:17PM +0800, Zha Bin wrote: > > > > > > From: Liu Jiang > > > > > >=20 > > > > > > The standard virtio-mmio devices use notification register to s= ignal > > > > > > backend. This will cause vmexits and slow down the > > > > > > performance when we > > > > > > passthrough the virtio-mmio devices to guest virtual machines. > > > > > > We proposed to update virtio over MMIO spec to add the per-queu= e > > > > > > notify feature VIRTIO_F_MMIO_NOTIFICATION[1]. It can allow the = VMM to > > > > > > configure notify location for each queue. > > > > > >=20 > > > > > > [1]https://lkml.org/lkml/2020/1/21/31 > > > > > >=20 > > > > > > Signed-off-by: Liu Jiang > > > > > > Co-developed-by: Zha Bin > > > > > > Signed-off-by: Zha Bin > > > > > > Co-developed-by: Jing Liu > > > > > > Signed-off-by: Jing Liu > > > > > > Co-developed-by: Chao Peng > > > > > > Signed-off-by: Chao Peng > > > > > Hmm. Any way to make this static so we don't need > > > > > base and multiplier? > > > > E.g page per vq? > > > >=20 > > > > Thanks > > > Problem is, is page size well defined enough? > > > Are there cases where guest and host page sizes differ? > > > I suspect there might be. > >=20 > >=20 > > Right, so it looks better to keep base and multiplier, e.g for vDPA. > >=20 > >=20 > > >=20 > > > But I also think this whole patch is unproven. Is someone actually > > > working on QEMU code to support pass-trough of virtio-pci > > > as virtio-mmio for nested guests? What's the performance > > > gain like? > >=20 > >=20 > > I don't know. > >=20 > > Thanks >=20 >=20 > Btw, I think there's no need for a nested environment to test. Current > eventfd hook to MSIX should still work for MMIO. >=20 > Thanks Oh yes it's the wildcard thingy but how much extra performance does one get from it with MMIO? A couple % might not be worth the trouble for MMIO. --=20 MST