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Subject: Re: [virtio-comment] Re: [PATCH v3 6/8] admin: Add theory of operation for write recording commands
On 11/15/2023 4:05 PM, Michael S. Tsirkin wrote:
On Wed, Nov 15, 2023 at 03:59:16PM +0800, Zhu, Lingshan wrote:On 11/15/2023 3:51 PM, Michael S. Tsirkin wrote:On Wed, Nov 15, 2023 at 12:05:59PM +0800, Zhu, Lingshan wrote:On 11/14/2023 4:27 PM, Michael S. Tsirkin wrote:On Tue, Nov 14, 2023 at 03:34:32PM +0800, Zhu, Lingshan wrote:So I can't believe it has good performance overall. Logging via IOMMU or using shadow virtqueue doesn't need any extra PCI transactions at least.On the other hand they have an extra CPU cost. Personally if this is coming from a hardware vendor, I am inclined to trust them wrt PCI transactions. But anyway, discussing this at a high level theoretically is pointless - whoever bothers with actual prototyping for performance testing wins, if no one does I'd expect a back of a napkin estimate to be included.if so, Intel has released productions implementing these interfaces years ago, see live migration in 4.1. IFCVF vDPA Implementation, https://doc.dpdk.org/guides-21.11/vdpadevs/ifc.html andThat one is based on shadow queue, right? Which I think this shows is worth supporting.Yes, it is shadow virtqueue, I assume this is already mostly done, do you see any gaps we need to address in our series that we should work on? ThanksThere were a ton of comments posted on your series.Hope I didn't miss anything. I see your latest comments are about vq states, as replied before, I think we can record the states by two le16 and the in-flight descriptor tracking facility.I don't know why you need the le16. in-flight tracking should be enough. And given it needs DMA I would try really hard to actually use admin commands for this.
we need to record the on-device avail_idx and used_idx, or how can the destination side know the device internal values.
On a second thought, shadow vqs are hypervisor behaviors, maybe should not beFor this shadow virtqueue, do you think I should address this in my V4? Like saying: acknowledged control commands through the control virtqueue should be recorded, and we want to use shadow virtqueue to track dirty pages.What you need to do is actually describe what do you expect the device to do when it enters this suspend state. since you mention control virtqueue then it seems that there needs to be a device type specific text explaining the behaviour. If so this implies there needs to be a list of device types that support suspend until someone looks at each type and documents what it does.
described in this device spec.Since SUSPEND is in device status, so for now I see every type of device implements
device_status should support SUSPEND. This should be a general facility.
But I still believe we are here try our best to work out an industrial spec with better quality, to serve broad interest. This is not competition between companies, and the spec is not a FIFO, not like a early bird can catch all the worm.This publicly archived list offers a means to provide input to the OASIS Virtual I/O Device (VIRTIO) TC. In order to verify user consent to the Feedback License terms and to minimize spam in the list archive, subscription is required before posting. Subscribe: virtio-comment-subscribe@lists.oasis-open.org Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org List help: virtio-comment-help@lists.oasis-open.org List archive: https://lists.oasis-open.org/archives/virtio-comment/ Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists Committee: https://www.oasis-open.org/committees/virtio/ Join OASIS: https://www.oasis-open.org/join/
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