Re: [PATCH 1/7] vfio/sdmdev: Add documents for WarpDrive framework

[Randy Dunlap]

Hi,

On 09/02/2018 05:51 PM, Kenneth Lee wrote:
> From: Kenneth Lee <liguozhu@xxxxxxxxxxxxx>
> 
> WarpDrive is a common user space accelerator framework.  Its main component
> in Kernel is called sdmdev, Share Domain Mediated Device. It exposes
> the hardware capabilities to the user space via vfio-mdev. So processes in
> user land can obtain a "queue" by open the device and direct access the
> hardware MMIO space or do DMA operation via VFIO interface.
> 
> WarpDrive is intended to be used with Jean Philippe Brucker's SVA
> patchset to support multi-process. But This is not a must.  Without the
> SVA patches, WarpDrive can still work for one process for every hardware
> device.
> 
> This patch add detail documents for the framework.
> 
> Signed-off-by: Kenneth Lee <liguozhu@xxxxxxxxxxxxx>
> ---
>  Documentation/00-INDEX                |   2 +
>  Documentation/warpdrive/warpdrive.rst | 100 ++++
>  Documentation/warpdrive/wd-arch.svg   | 728 ++++++++++++++++++++++++++
>  3 files changed, 830 insertions(+)
>  create mode 100644 Documentation/warpdrive/warpdrive.rst
>  create mode 100644 Documentation/warpdrive/wd-arch.svg

> diff --git a/Documentation/warpdrive/warpdrive.rst b/Documentation/warpdrive/warpdrive.rst
> new file mode 100644
> index 000000000000..6d2a5d1e08c4
> --- /dev/null
> +++ b/Documentation/warpdrive/warpdrive.rst
> @@ -0,0 +1,100 @@
> +Introduction of WarpDrive
> +=========================
> +
> +*WarpDrive* is a general accelerator framework for user space. It intends to
> +provide interface for the user process to send request to hardware
> +accelerator without heavy user-kernel interaction cost.
> +
> +The *WarpDrive* user library is supposed to provide a pipe-based API, such as:

Do you say "is supposed to" because it doesn't do that (yet)?
Or you could just change that to say:

   The WarpDrive user library provides a pipe-based API, such as:


> +        ::
> +        int wd_request_queue(struct wd_queue *q);
> +        void wd_release_queue(struct wd_queue *q);
> +
> +        int wd_send(struct wd_queue *q, void *req);
> +        int wd_recv(struct wd_queue *q, void **req);
> +        int wd_recv_sync(struct wd_queue *q, void **req);
> +        int wd_flush(struct wd_queue *q);
> +
> +*wd_request_queue* creates the pipe connection, *queue*, between the
> +application and the hardware. The application sends request and pulls the
> +answer back by asynchronized wd_send/wd_recv, which directly interact with the
> +hardware (by MMIO or share memory) without syscall.
> +
> +*WarpDrive* maintains a unified application address space among all involved
> +accelerators.  With the following APIs: ::

Seems like an extra '.' there.  How about:

  accelerators with the following APIs: ::

> +
> +        int wd_mem_share(struct wd_queue *q, const void *addr,
> +                         size_t size, int flags);
> +        void wd_mem_unshare(struct wd_queue *q, const void *addr, size_t size);
> +
> +The referred process space shared by these APIs can be directly referred by the
> +hardware. The process can also dedicate its whole process space with flags,
> +*WD_SHARE_ALL* (not in this patch yet).
> +
> +The name *WarpDrive* is simply a cool and general name meaning the framework
> +makes the application faster. As it will be explained in this text later, the
> +facility in kernel is called *SDMDEV*, namely "Share Domain Mediated Device".
> +
> +
> +How does it work
> +================
> +
> +*WarpDrive* is built upon *VFIO-MDEV*. The queue is wrapped as *mdev* in VFIO.
> +So memory sharing can be done via standard VFIO standard DMA interface.
> +
> +The architecture is illustrated as follow figure:
> +
> +.. image:: wd-arch.svg
> +        :alt: WarpDrive Architecture
> +
> +Accelerator driver shares its capability via *SDMDEV* API: ::
> +
> +        vfio_sdmdev_register(struct vfio_sdmdev *sdmdev);
> +        vfio_sdmdev_unregister(struct vfio_sdmdev *sdmdev);
> +        vfio_sdmdev_wake_up(struct spimdev_queue *q);
> +
> +*vfio_sdmdev_register* is a helper function to register the hardware to the
> +*VFIO_MDEV* framework. The queue creation is done by *mdev* creation interface.
> +
> +*WarpDrive* User library mmap the mdev to access its mmio space and shared

s/mmio/MMIO/

> +memory. Request can be sent to, or receive from, hardware in this mmap-ed
> +space until the queue is full or empty.
> +
> +The user library can wait on the queue by ioctl(VFIO_SDMDEV_CMD_WAIT) the mdev
> +if the queue is full or empty. If the queue status is changed, the hardware
> +driver use *vfio_sdmdev_wake_up* to wake up the waiting process.
> +
> +
> +Multiple processes support
> +==========================
> +
> +In the latest mainline kernel (4.18) when this document is written,
> +multi-process is not supported in VFIO yet.
> +
> +Jean Philippe Brucker has a patchset to enable it[1]_. We have tested it
> +with our hardware (which is known as *D06*). It works well. *WarpDrive* rely
> +on them to support multiple processes. If it is not enabled, *WarpDrive* can
> +still work, but it support only one mdev for a process, which will share the
> +same io map table with kernel. (But it is not going to be a security problem,
> +since the user application cannot access the kernel address space)
> +
> +When multiprocess is support, mdev can be created based on how many
> +hardware resource (queue) is available. Because the VFIO framework accepts only
> +one open from one mdev iommu_group. Mdev become the smallest unit for process
> +to use queue. And the mdev will not be released if the user process exist. So
> +it will need a resource agent to manage the mdev allocation for the user
> +process. This is not in this document's range.
> +
> +
> +Legacy Mode Support
> +===================
> +For the hardware on which IOMMU is not support, WarpDrive can run on *NOIOMMU*
> +mode. That require some update to the mdev driver, which is not included in
> +this version yet.
> +
> +
> +References
> +==========
> +.. [1] https://patchwork.kernel.org/patch/10394851/
> +
> +.. vim: tw=78

thanks,
-- 
~Randy