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    SubjectRe: [PATCH v2 1/5] virtio-mmio: add notify feature for per-queue
    On Wed, Feb 12, 2020 at 11:39:54AM +0800, Jason Wang wrote:
    >
    > On 2020/2/11 下午7:33, Michael S. Tsirkin wrote:
    > > On Mon, Feb 10, 2020 at 05:05:17PM +0800, Zha Bin wrote:
    > > > From: Liu Jiang<gerry@linux.alibaba.com>
    > > >
    > > > The standard virtio-mmio devices use notification register to signal
    > > > 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-queue
    > > > notify feature VIRTIO_F_MMIO_NOTIFICATION[1]. It can allow the VMM to
    > > > configure notify location for each queue.
    > > >
    > > > [1]https://lkml.org/lkml/2020/1/21/31
    > > >
    > > > Signed-off-by: Liu Jiang<gerry@linux.alibaba.com>
    > > > Co-developed-by: Zha Bin<zhabin@linux.alibaba.com>
    > > > Signed-off-by: Zha Bin<zhabin@linux.alibaba.com>
    > > > Co-developed-by: Jing Liu<jing2.liu@linux.intel.com>
    > > > Signed-off-by: Jing Liu<jing2.liu@linux.intel.com>
    > > > Co-developed-by: Chao Peng<chao.p.peng@linux.intel.com>
    > > > Signed-off-by: Chao Peng<chao.p.peng@linux.intel.com>
    > > Hmm. Any way to make this static so we don't need
    > > base and multiplier?
    >
    >
    > E.g page per vq?
    >
    > Thanks

    Problem is, is page size well defined enough?
    Are there cases where guest and host page sizes differ?
    I suspect there might be.

    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?

    --
    MST

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