Messages in this thread | | | Subject | Re: [virtio-dev] Re: [PATCH v2 4/5] virtio-mmio: add MSI interrupt feature support | From | Jason Wang <> | Date | Tue, 11 Feb 2020 12:02:50 +0800 |
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On 2020/2/11 上午11:35, 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<gerry@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
I think you need add more comments on the command.
E.g if I want to map vector 0 to queue 1, how do I need to do?
write(1, queue_sel); write(0, vector_sel);
?
Thanks
> > >> Thanks >> >> >> >> --------------------------------------------------------------------- >> To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org >> For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org >> >
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