On Wed, Feb 12, 2020 at 05:33:06PM +0800, Jason Wang wrote: > > On 2020/2/12 下午4:53, Jason Wang wrote: > > > > On 2020/2/12 下午4:18, Michael S. Tsirkin wrote: > > > 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<ge...@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<ge...@linux.alibaba.com> > > > > > > Co-developed-by: Zha Bin<zha...@linux.alibaba.com> > > > > > > Signed-off-by: Zha Bin<zha...@linux.alibaba.com> > > > > > > Co-developed-by: Jing Liu<jing2....@linux.intel.com> > > > > > > Signed-off-by: Jing Liu<jing2....@linux.intel.com> > > > > > > Co-developed-by: Chao Peng<chao.p.p...@linux.intel.com> > > > > > > Signed-off-by: Chao Peng<chao.p.p...@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. > > > > > > 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
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. -- MST
