From: Jason Wang <jasowang@redhat.com>
To: Kishon Vijay Abraham I <kishon@ti.com>,
Cornelia Huck <cohuck@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
Ohad Ben-Cohen <ohad@wizery.com>,
Bjorn Andersson <bjorn.andersson@linaro.org>,
Jon Mason <jdmason@kudzu.us>, Dave Jiang <dave.jiang@intel.com>,
Allen Hubbe <allenbh@gmail.com>,
Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
Bjorn Helgaas <bhelgaas@google.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Stefan Hajnoczi <stefanha@redhat.com>,
Stefano Garzarella <sgarzare@redhat.com>,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-remoteproc@vger.kernel.org, linux-ntb@googlegroups.com,
linux-pci@vger.kernel.org, kvm@vger.kernel.org,
virtualization@lists.linux-foundation.org,
netdev@vger.kernel.org
Subject: Re: [RFC PATCH 00/22] Enhance VHOST to enable SoC-to-SoC communication
Date: Wed, 16 Sep 2020 11:10:50 +0800 [thread overview]
Message-ID: <ee0aa81d-064b-d7a7-86bb-79a3f4d3dd11@redhat.com> (raw)
In-Reply-To: <181ae83d-edeb-9406-27cc-1195fe29ae95@ti.com>
On 2020/9/15 下午11:47, Kishon Vijay Abraham I wrote:
> Hi Jason,
>
> On 15/09/20 1:48 pm, Jason Wang wrote:
>> Hi Kishon:
>>
>> On 2020/9/14 下午3:23, Kishon Vijay Abraham I wrote:
>>>> Then you need something that is functional equivalent to virtio PCI
>>>> which is actually the concept of vDPA (e.g vDPA provides alternatives if
>>>> the queue_sel is hard in the EP implementation).
>>> Okay, I just tried to compare the 'struct vdpa_config_ops' and 'struct
>>> vhost_config_ops' ( introduced in [RFC PATCH 03/22] vhost: Add ops for
>>> the VHOST driver to configure VHOST device).
>>>
>>> struct vdpa_config_ops {
>>> /* Virtqueue ops */
>>> int (*set_vq_address)(struct vdpa_device *vdev,
>>> u16 idx, u64 desc_area, u64 driver_area,
>>> u64 device_area);
>>> void (*set_vq_num)(struct vdpa_device *vdev, u16 idx, u32 num);
>>> void (*kick_vq)(struct vdpa_device *vdev, u16 idx);
>>> void (*set_vq_cb)(struct vdpa_device *vdev, u16 idx,
>>> struct vdpa_callback *cb);
>>> void (*set_vq_ready)(struct vdpa_device *vdev, u16 idx, bool ready);
>>> bool (*get_vq_ready)(struct vdpa_device *vdev, u16 idx);
>>> int (*set_vq_state)(struct vdpa_device *vdev, u16 idx,
>>> const struct vdpa_vq_state *state);
>>> int (*get_vq_state)(struct vdpa_device *vdev, u16 idx,
>>> struct vdpa_vq_state *state);
>>> struct vdpa_notification_area
>>> (*get_vq_notification)(struct vdpa_device *vdev, u16 idx);
>>> /* vq irq is not expected to be changed once DRIVER_OK is set */
>>> int (*get_vq_irq)(struct vdpa_device *vdv, u16 idx);
>>>
>>> /* Device ops */
>>> u32 (*get_vq_align)(struct vdpa_device *vdev);
>>> u64 (*get_features)(struct vdpa_device *vdev);
>>> int (*set_features)(struct vdpa_device *vdev, u64 features);
>>> void (*set_config_cb)(struct vdpa_device *vdev,
>>> struct vdpa_callback *cb);
>>> u16 (*get_vq_num_max)(struct vdpa_device *vdev);
>>> u32 (*get_device_id)(struct vdpa_device *vdev);
>>> u32 (*get_vendor_id)(struct vdpa_device *vdev);
>>> u8 (*get_status)(struct vdpa_device *vdev);
>>> void (*set_status)(struct vdpa_device *vdev, u8 status);
>>> void (*get_config)(struct vdpa_device *vdev, unsigned int offset,
>>> void *buf, unsigned int len);
>>> void (*set_config)(struct vdpa_device *vdev, unsigned int offset,
>>> const void *buf, unsigned int len);
>>> u32 (*get_generation)(struct vdpa_device *vdev);
>>>
>>> /* DMA ops */
>>> int (*set_map)(struct vdpa_device *vdev, struct vhost_iotlb *iotlb);
>>> int (*dma_map)(struct vdpa_device *vdev, u64 iova, u64 size,
>>> u64 pa, u32 perm);
>>> int (*dma_unmap)(struct vdpa_device *vdev, u64 iova, u64 size);
>>>
>>> /* Free device resources */
>>> void (*free)(struct vdpa_device *vdev);
>>> };
>>>
>>> +struct vhost_config_ops {
>>> + int (*create_vqs)(struct vhost_dev *vdev, unsigned int nvqs,
>>> + unsigned int num_bufs, struct vhost_virtqueue *vqs[],
>>> + vhost_vq_callback_t *callbacks[],
>>> + const char * const names[]);
>>> + void (*del_vqs)(struct vhost_dev *vdev);
>>> + int (*write)(struct vhost_dev *vdev, u64 vhost_dst, void *src,
>>> int len);
>>> + int (*read)(struct vhost_dev *vdev, void *dst, u64 vhost_src, int
>>> len);
>>> + int (*set_features)(struct vhost_dev *vdev, u64 device_features);
>>> + int (*set_status)(struct vhost_dev *vdev, u8 status);
>>> + u8 (*get_status)(struct vhost_dev *vdev);
>>> +};
>>> +
>>> struct virtio_config_ops
>>> I think there's some overlap here and some of the ops tries to do the
>>> same thing.
>>>
>>> I think it differs in (*set_vq_address)() and (*create_vqs)().
>>> [create_vqs() introduced in struct vhost_config_ops provides
>>> complimentary functionality to (*find_vqs)() in struct
>>> virtio_config_ops. It seemingly encapsulates the functionality of
>>> (*set_vq_address)(), (*set_vq_num)(), (*set_vq_cb)(),..].
>>>
>>> Back to the difference between (*set_vq_address)() and (*create_vqs)(),
>>> set_vq_address() directly provides the virtqueue address to the vdpa
>>> device but create_vqs() only provides the parameters of the virtqueue
>>> (like the number of virtqueues, number of buffers) but does not directly
>>> provide the address. IMO the backend client drivers (like net or vhost)
>>> shouldn't/cannot by itself know how to access the vring created on
>>> virtio front-end. The vdpa device/vhost device should have logic for
>>> that. That will help the client drivers to work with different types of
>>> vdpa device/vhost device and can access the vring created by virtio
>>> irrespective of whether the vring can be accessed via mmio or kernel
>>> space or user space.
>>>
>>> I think vdpa always works with client drivers in userspace and providing
>>> userspace address for vring.
>>
>> Sorry for being unclear. What I meant is not replacing vDPA with the
>> vhost(bus) you proposed but the possibility of replacing virtio-pci-epf
>> with vDPA in:
> Okay, so the virtio back-end still use vhost and front end should use
> vDPA. I see. So the host side PCI driver for EPF should populate
> vdpa_config_ops and invoke vdpa_register_device().
Yes.
>> My question is basically for the part of virtio_pci_epf_send_command(),
>> so it looks to me you have a vendor specific API to replace the
>> virtio-pci layout of the BAR:
> Even when we use vDPA, we have to use some sort of
> virtio_pci_epf_send_command() to communicate with virtio backend right?
Right.
>
> Right, the layout is slightly different from the standard layout.
>
> This is the layout
> struct epf_vhost_reg_queue {
> u8 cmd;
> u8 cmd_status;
> u16 status;
> u16 num_buffers;
> u16 msix_vector;
> u64 queue_addr;
What's the meaning of queue_addr here?
Does not mean the device expects a contiguous memory for avail/desc/used
ring?
> } __packed;
>
> struct epf_vhost_reg {
> u64 host_features;
> u64 guest_features;
> u16 msix_config;
> u16 num_queues;
> u8 device_status;
> u8 config_generation;
> u32 isr;
> u8 cmd;
> u8 cmd_status;
> struct epf_vhost_reg_queue vq[MAX_VQS];
> } __packed;
>>
>> +static int virtio_pci_epf_send_command(struct virtio_pci_device *vp_dev,
>> + u32 command)
>> +{
>> + struct virtio_pci_epf *pci_epf;
>> + void __iomem *ioaddr;
>> + ktime_t timeout;
>> + bool timedout;
>> + int ret = 0;
>> + u8 status;
>> +
>> + pci_epf = to_virtio_pci_epf(vp_dev);
>> + ioaddr = vp_dev->ioaddr;
>> +
>> + mutex_lock(&pci_epf->lock);
>> + writeb(command, ioaddr + HOST_CMD);
>> + timeout = ktime_add_ms(ktime_get(), COMMAND_TIMEOUT);
>> + while (1) {
>> + timedout = ktime_after(ktime_get(), timeout);
>> + status = readb(ioaddr + HOST_CMD_STATUS);
>> +
>>
>> Several questions:
>>
>> - It's not clear to me how the synchronization is done between the RC
>> and EP. E.g how and when the value of HOST_CMD_STATUS can be changed.
> The HOST_CMD (commands sent to the EP) is serialized by using mutex.
> Once the EP reads the command, it resets the value in HOST_CMD. So
> HOST_CMD is less likely an issue.
Here's my understanding of the protocol:
1) RC write to HOST_CMD
2) RC wait for HOST_CMD_STATUS to be HOST_CMD_STATUS_OKAY
It looks to me what EP should do is
1) EP reset HOST_CMD after reading new command
And it looks to me EP should also reset HOST_CMD_STATUS here?
(I thought there should be patch to handle stuffs like this but I didn't
find it in this series)
>
> A sufficiently large time is given for the EP to complete it's operation
> (1 Sec) where the EP provides the status in HOST_CMD_STATUS. After it
> expires, HOST_CMD_STATUS_NONE is written to HOST_CMD_STATUS. There could
> be case where EP updates HOST_CMD_STATUS after RC writes
> HOST_CMD_STATUS_NONE, but by then HOST has already detected this as
> failure and error-ed out.
>
>> If you still want to introduce a new transport, a virtio spec patch
>> would be helpful for us to understand the device API.
> Okay, that should be on https://github.com/oasis-tcs/virtio-spec.git?
Yes.
>> - You have you vendor specific layout (according to
>> virtio_pci_epb_table()), so I guess you it's better to have a vendor
>> specific vDPA driver instead
> Okay, with vDPA, we are free to define our own layouts.
Right, but vDPA have other requirements. E.g it requires the device have
the ability to save/restore the state (e.g the last_avail_idx).
So it actually depends on what you want. If you don't care about
userspace drivers and want to have a standard transport, you can still
go virtio.
>> - The advantage of vendor specific vDPA driver is that it can 1) have
>> less codes 2) support userspace drivers through vhost-vDPA (instead of
>> inventing new APIs since we can't use vfio-pci here).
> I see there's an additional level of indirection from virtio to vDPA and
> probably no need for spec update but don't exactly see how it'll reduce
> code.
AFAIK you don't need to implement your own setup_vq and del_vq.
>
> For 2, Isn't vhost-vdpa supposed to run on virtio backend?
Not currently, vDPA is a superset of virtio (e.g it support virtqueue
state save/restore). This it should be possible in the future probably.
>
> From a high level, I think I should be able to use vDPA for
> virtio_pci_epf.c. Would you also suggest using vDPA for ntb_virtio.c?
> ([RFC PATCH 20/22] NTB: Add a new NTB client driver to implement VIRTIO
> functionality).
I think it's your call. If you want
1) a well-defined standard virtio transport
2) willing to finalize d and maintain the spec
3) doesn't care about userspace drivers
You can go with virtio, otherwise vDPA.
Thanks
>
> Thanks
> Kishon
>
next prev parent reply other threads:[~2020-09-16 3:11 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-02 8:21 [RFC PATCH 00/22] Enhance VHOST to enable SoC-to-SoC communication Kishon Vijay Abraham I
2020-07-02 8:21 ` [RFC PATCH 01/22] vhost: Make _feature_ bits a property of vhost device Kishon Vijay Abraham I
2020-07-02 8:21 ` [RFC PATCH 02/22] vhost: Introduce standard Linux driver model in VHOST Kishon Vijay Abraham I
2020-07-02 8:21 ` [RFC PATCH 03/22] vhost: Add ops for the VHOST driver to configure VHOST device Kishon Vijay Abraham I
2020-07-02 8:21 ` [RFC PATCH 04/22] vringh: Add helpers to access vring in MMIO Kishon Vijay Abraham I
2020-07-02 8:21 ` [RFC PATCH 05/22] vhost: Add MMIO helpers for operations on vhost virtqueue Kishon Vijay Abraham I
2020-07-02 8:21 ` [RFC PATCH 06/22] vhost: Introduce configfs entry for configuring VHOST Kishon Vijay Abraham I
2020-07-02 8:21 ` [RFC PATCH 07/22] virtio_pci: Use request_threaded_irq() instead of request_irq() Kishon Vijay Abraham I
2020-07-02 8:21 ` [RFC PATCH 08/22] rpmsg: virtio_rpmsg_bus: Disable receive virtqueue callback when reading messages Kishon Vijay Abraham I
2020-07-02 8:21 ` [RFC PATCH 09/22] rpmsg: Introduce configfs entry for configuring rpmsg Kishon Vijay Abraham I
2020-07-02 8:21 ` [RFC PATCH 10/22] rpmsg: virtio_rpmsg_bus: Add Address Service Notification support Kishon Vijay Abraham I
2020-07-02 8:21 ` [RFC PATCH 11/22] rpmsg: virtio_rpmsg_bus: Move generic rpmsg structure to rpmsg_internal.h Kishon Vijay Abraham I
2020-07-02 8:21 ` [RFC PATCH 12/22] virtio: Add ops to allocate and free buffer Kishon Vijay Abraham I
2020-07-02 8:21 ` [RFC PATCH 13/22] rpmsg: virtio_rpmsg_bus: Use virtio_alloc_buffer() and virtio_free_buffer() Kishon Vijay Abraham I
2020-07-02 8:21 ` [RFC PATCH 14/22] rpmsg: Add VHOST based remote processor messaging bus Kishon Vijay Abraham I
2020-07-02 8:21 ` [RFC PATCH 15/22] samples/rpmsg: Setup delayed work to send message Kishon Vijay Abraham I
2020-07-02 8:21 ` [RFC PATCH 16/22] samples/rpmsg: Wait for address to be bound to rpdev for sending message Kishon Vijay Abraham I
2020-07-02 8:21 ` [RFC PATCH 17/22] rpmsg.txt: Add Documentation to configure rpmsg using configfs Kishon Vijay Abraham I
2020-07-02 8:21 ` [RFC PATCH 18/22] virtio_pci: Add VIRTIO driver for VHOST on Configurable PCIe Endpoint device Kishon Vijay Abraham I
2020-07-02 8:21 ` [RFC PATCH 19/22] PCI: endpoint: Add EP function driver to provide VHOST interface Kishon Vijay Abraham I
2020-07-02 8:21 ` [RFC PATCH 20/22] NTB: Add a new NTB client driver to implement VIRTIO functionality Kishon Vijay Abraham I
2020-07-02 8:21 ` [RFC PATCH 21/22] NTB: Add a new NTB client driver to implement VHOST functionality Kishon Vijay Abraham I
2020-07-02 8:21 ` [RFC PATCH 22/22] NTB: Describe ntb_virtio and ntb_vhost client in the documentation Kishon Vijay Abraham I
2020-07-02 9:51 ` [RFC PATCH 00/22] Enhance VHOST to enable SoC-to-SoC communication Michael S. Tsirkin
2020-07-02 10:10 ` Jason Wang
2020-07-02 13:35 ` Kishon Vijay Abraham I
2020-07-03 7:16 ` Jason Wang
2020-07-06 9:32 ` Kishon Vijay Abraham I
2020-07-07 9:47 ` Jason Wang
2020-07-07 14:45 ` Kishon Vijay Abraham I
2020-07-08 11:22 ` Jason Wang
2020-07-08 13:13 ` Kishon Vijay Abraham I
2020-07-09 6:26 ` Jason Wang
2020-08-28 10:34 ` Cornelia Huck
2020-09-01 5:24 ` Kishon Vijay Abraham I
2020-09-01 8:50 ` Jason Wang
2020-09-08 16:37 ` Cornelia Huck
2020-09-09 8:41 ` Jason Wang
2020-09-14 7:23 ` Kishon Vijay Abraham I
2020-09-15 8:18 ` Jason Wang
2020-09-15 15:47 ` Kishon Vijay Abraham I
2020-09-16 3:10 ` Jason Wang [this message]
2020-09-16 11:47 ` Kishon Vijay Abraham I
2020-09-16 11:47 ` Kishon Vijay Abraham I
2020-09-18 4:04 ` Jason Wang
2020-07-15 17:15 ` Mathieu Poirier
2020-09-01 4:40 ` Kishon Vijay Abraham I
2020-07-02 10:25 ` Kishon Vijay Abraham I
2020-07-02 17:31 ` Mathieu Poirier
2020-07-03 6:17 ` Kishon Vijay Abraham I
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