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Subject: Re: [PATCH v2 1/5] virtio-mmio: add notify feature for per-queue
On 2020/2/12 äå4:53, Jason Wang wrote:
On 2020/2/12 äå4:18, Michael S. Tsirkin wrote:On Wed, Feb 12, 2020 at 11:39:54AM +0800, Jason Wang wrote:On 2020/2/11 äå7:33, 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 signalbackend. This will cause vmexits and slow down the performance when wepassthrough 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? ThanksProblem is, is page size well defined enough? Are there cases where guest and host page sizes differ? I suspect there might be.Right, so it looks better to keep base and multiplier, e.g for vDPA.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?I don't know. Thanks
Btw, I think there's no need for a nested environment to test. Current eventfd hook to MSIX should still work for MMIO.
Thanks
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