On Tue, Feb 11, 2020 at 11:35:43AM +0800, Liu, Jing2 wrote: > > On 2/11/2020 11:17 AM, Jason Wang wrote: > > > > On 2020/2/10 下午5:05, Zha Bin wrote: > > > From: Liu Jiang<ge...@linux.alibaba.com> > > > > > > Userspace VMMs (e.g. Qemu microvm, Firecracker) take advantage of using > > > virtio over mmio devices as a lightweight machine model for modern > > > cloud. The standard virtio over MMIO transport layer only supports one > > > legacy interrupt, which is much heavier than virtio over PCI transport > > > layer using MSI. Legacy interrupt has long work path and causes specific > > > VMExits in following cases, which would considerably slow down the > > > performance: > > > > > > 1) read interrupt status register > > > 2) update interrupt status register > > > 3) write IOAPIC EOI register > > > > > > We proposed to add MSI support for virtio over MMIO via new feature > > > bit VIRTIO_F_MMIO_MSI[1] which increases the interrupt performance. > > > > > > With the VIRTIO_F_MMIO_MSI feature bit supported, the virtio-mmio MSI > > > uses msi_sharing[1] to indicate the event and vector mapping. > > > Bit 1 is 0: device uses non-sharing and fixed vector per event mapping. > > > Bit 1 is 1: device uses sharing mode and dynamic mapping. > > > > > > I believe dynamic mapping should cover the case of fixed vector? > > > Actually this bit *aims* for msi sharing or msi non-sharing. > > It means, when msi sharing bit is 1, device doesn't want vector per queue > > (it wants msi vector sharing as name) and doesn't want a high interrupt > rate. > > So driver turns to !per_vq_vectors and has to do dynamical mapping. > > So they are opposite not superset. > > Thanks! > > Jing
what's the point of all this flexibility? the cover letter complains about the code size of pci, then you go back and add a ton of options with no justification. > > > Thanks > > > > > > > > --------------------------------------------------------------------- > > To unsubscribe, e-mail: virtio-dev-unsubscr...@lists.oasis-open.org > > For additional commands, e-mail: virtio-dev-h...@lists.oasis-open.org > >
