From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Tue, 25 Jan 2022 07:09:07 -0500 From: "Michael S. Tsirkin" Subject: Re: [PATCH 2/5] Introduce VIRTIO_F_ADMIN_VQ_INDIRECT_DESC/VIRTIO_F_ADMIN_VQ_IN_ORDER Message-ID: <20220125070649-mutt-send-email-mst@kernel.org> References: <20220118011731-mutt-send-email-mst@kernel.org> <20220118014737-mutt-send-email-mst@kernel.org> <15063a94-85ae-fd1a-6ff1-458a039d1def@redhat.com> <56a7bf50-509d-f9d5-df78-858cb1b156c1@redhat.com> MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit To: Max Gurtovoy Cc: Parav Pandit , Jason Wang , "cohuck@redhat.com" , "virtio-dev@lists.oasis-open.org" , Shahaf Shuler , Oren Duer , "stefanha@redhat.com" List-ID: On Tue, Jan 25, 2022 at 12:59:16PM +0200, Max Gurtovoy wrote: > > On 1/25/2022 5:52 AM, Parav Pandit wrote: > > Hi Jason, > > > > > From: Jason Wang > > > Sent: Tuesday, January 25, 2022 8:59 AM > > > > > > 在 2022/1/19 下午12:48, Parav Pandit 写道: > > > > > From: Jason Wang > > > > > Sent: Wednesday, January 19, 2022 9:33 AM > > > > > > > > > > > > > > > It it means IMS, there's already a proposal[1] that introduce MSI > > > > > commands via the admin virtqueue. And we had similar requirement for > > > > > virtio-MMIO[2] and managed device or SF [3], so I would rather to > > > > > introduce IMS (need a better name though) as a basic facility instead > > > > > of tie it to any specific transport. > > > > > > > > > IMS of [1] is a interrupt configuration by the virtio driver for the device is it > > > driving, which needs a queue. > > > > So regardless of the device type as PCI PF/VF/SF/ADI, there is desire to have a > > > generic admin queue not attached to device type. > > > > And AQ in this proposal exactly serves this purpose. > > > > > > > > Device configuring its own IMS vector vs PCI PF configuring VF's MSI-X max > > > vector count are two different functionality. > > > > Both of these commands can ride on a generic queue. > > > > However the queue is not same, because PF owns its own admin queue > > > > (for vf msix config), VF or SF operates its own admin queue (for IMS > > > > config). > > > > > > So I think in the next version we need to clarify: > > > > > > 1) is there a single admin virtqueue shared by all the VFs and PF > > > > > > or > > > > > > 2) per VF/PF admin virtqueue, and how does the driver know how to find the > > > corresponding admin virtqueue > > > > > Admin queue is not per VF. > > Lets take concrete examples. > > 1. So for example, PCI PF can have one AQ. > > This AQ carries command to query/config MSI-X vector of VFs. > > > > 2. In second example, PCI PF is creating/destroying SFs. This is again done by using the AQ of the PCI PF. > > > > 3. A PCI VF has its own AQ to configure some of its own generic attribute, don't know which is that today. > > May be something that is extremely hard to do over features bit. > > Currently proposed v2 doesn't restrict admin queue to be within PCI PF or VF or that matter not limited to other transports. > > > > So a good example is, > > > > 1. PCI PF configures 8 MSI-X or 16 IMS vectors for the VF using PF_AQ in HV. > > > > 2. PCI VF when using IMS configures, IMS data, vector, mask etc using VF_AQ > > > in GVM. > > > > Both the functions will have AQ feature bit set. > > > > > > Where did the VF_AQ sit? I guess it belongs to the VF. But if this is > > > true, don't we need some kind of address isolation like PASID? > > > > > Above one for IMS is not a good example. I replied the reasoning last week for it. > > > > Fair enough, so we have more users of admin queue than just MSI-X config. > > > > > > Well, what I really meant is that we actually have more users of IMS. > > > That's is exactly what virito-mmio wants. In this case introducing admin > > > queue looks too heavyweight for that. > > > > > IMS config cannot be done over AQ as described in previous email in this thread. > > > > > > > > 2. AQ to follows IN_ORDER and INDIRECT_DESC negotiation like rest of > > > > > > the queues 3. Update commit log to describe why config space is not > > > > > > chosen (scale, on-die registers, uniform way to handle all aq cmds) > > > > > I fail to understand the scale/registeres issues. With the one of my previous > > > > > proposal (device selector), technically we don't even need any config space > > > or > > > > > BAR for VF or SF by multiplexing the registers for PF. > > > > > > > > > Scale issue is: when you want to create, query, manipulate hundreds of > > > objects, having shared MMIO register or configuration register, will be too > > > slow. > > > > > > > > > Ok, this need to be clarified in the commit log. And we need make sure > > > it's not an issue that is only happen for some specific vendor. > > It is present in the v2 commit log cover letter. > > Please let me know if you think it should be in the actual patch commit log. > > > > > > > > And additionally such register set doesn't scale to allow sharing large > > > number of bytes as DMA cannot be done. > > > > > > > > > That's true. > > > > > > > > > > From physical device perspective, it doesn’t scale because device needs to > > > have those resources ready to answer on MMIO reads and for hundreds to > > > thousand of devices it just cannot do it. > > > > This is one of the reason for birth of IMS. > > > > > > IMS allows the table to be stored in the memory and cached by the device > > > to have the best scalability. But I had other questions: > > > > > > 1) if we have a single admin virtqueue, there will still be contention > > > in the driver side > > > > > AQ inherently allows out of order commands execution. > > It shouldn't face contention. For example 1K depth AQ should be serving hundreds of descriptors commands in parallel for SF creation, VF MSI-X config and more. > > > > Which area/commands etc you think can lead to the contention? > > > 2) if we have per vf admin virtqueue, it still doesn't scale since it > > > occupies more hardware resources > > > > > That is too heavy, and doesn’t scale. Proposal is to not have per vf admin queue. > > Proposal is to have one admin queue in a virtio device. > > Right ? where did we mention something that can imply otherwise ? > > > > > > > I do see one advantage is that the admin virtqueue is transport > > > independent > > > > > (or it could be used as a transport). > > > > > > > > > I am yet to read the transport part from [1]. > > > > > > Yes, the main goal is to be compatible with SIOV. > > > > > Admin queue is a command interface transport where higher layer services can be buit. > > This includes SR-IOV config, SIOV config. > > And v2 enables SIOV commands implementation whenever they are ready. > > > > > > > > 4. Improve documentation around msix config to link to sriov section of > > > virtio > > > > > spec > > > > > > 5. Describe error that if VF is bound to the device, admin commands > > > > > targeting VF can fail, describe this error code > > > > > > Did I miss anything? > > > > > > > > > > > > Yet to receive your feedback on group, if/why is it needed and, why/if it > > > must > > > > > be in this proposal, what pieces prevents it do as follow-on. > > > > > > Cornelia, Jason, > > > > > > Can you please review current proposal as well before we revise v2? > > > > > If I understand correctly, most of the features (except for the admin > > > > > virtqueue in_order stuffs) are not specific to the admin virtqueue. As > > > > > discussed in the previous versions, I still think it's better: > > > > > > > > > > 1) adding sections in the basic device facility or data structure for > > > > > provisioning and MSI > > > > > 2) introduce admin virtqueue on top as an device interface for those > > > > > features > > > > > > > > > I didn't follow your suggestion. Can you please explain? > > > > Specifically "data structure for provisioning and MSI".. > > > > > > I meant: > > > > > > There's a chapter "Basic Facilities of a Virtio Device", we can > > > introduce the concepts there like: > > > > > > 1) Managed device and Management device (terminology proposed by > > > Michael), and can use PF and VF as a example > > > > > > 2) Managed device provisioning (the data structure to specify the > > > attributes of a managed device (VF)) > > > > > > 3) MSI > > > > > Above is good idea. Will revisit v2, if it is not arranged this way. > > Let me make sure I understand, you would like to see a new chapter under > "Basic Facilities of a Virtio Device" that is > > called "Device management" and this chapter will explain in few words the > concept and it will point to another chapter under "Basic Facilities of a > Virtio Device" > > that was introduced here "Admin Virtqueues" ? > > So you do agree that managing a managed (create/destroy/setup/etc...) will > be done using the AQ of the managing device ? I think Jason asked that the management commands are split from the queue itself, such that they can be implemented in more ways down the road. > > > And then we can introduced admin virtqueue in either > > > > > > 1) transport part > > > > > > or > > > > > > 2) PCI transport > > > > > It is not specific to PCI transport, and currently it is not a transport either. > > So admin queue will keep as general entity for admin work. > > > In the admin virtqueue, there will be commands to provision and > > > configure MSI. > > > > > Please review v2 if it is not arranged this way. > > > > > > > The leaves the chance for future extensions to allow those features to > > > > > be used by transport specific interface which will benefit for > > > > > > > > > AQ allows communication (command, response) between driver and device > > > in transport independent way. > > > > Sometimes it query/set transport specific fields like MSI-X vectors of VF. > > > > Sometimes device configure its on IMS interrupt. > > > > Something else in future. > > > > So it is really a generic request-response queue. > > > > > > I agree, but I think we can't mandate new features to a specific transport. > > > > > Certainly. Admin queue is transport independent. > > PCI MSI-X configuration is PCI transport specific command, so structures are defined it accordingly. > > It is similar to struct virtio_pci_cap, struct virtio_pci_common_cfg etc. > > > > Any other transport will have transport specific interrupt configuration. So it will be defined accordingly whenever that occurs. > > For example, IMS for VF or IMS for SF.