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

Kenneth Lee
2018-09-07T02:23:15Z

On Thu, Sep 06, 2018 at 11:36:36AM -0700, Randy Dunlap wrote:
> Date: Thu, 6 Sep 2018 11:36:36 -0700
> From: Randy Dunlap <rdunlap@infradead.org>
> To: Kenneth Lee <nek.in.cn@gmail.com>, Jonathan Corbet <corbet@lwn.net>,
> Herbert Xu <herbert@gondor.apana.org.au>, "David S . Miller"
> <davem@davemloft.net>, Joerg Roedel <joro@8bytes.org>, Alex Williamson
> <alex.williamson@redhat.com>, Kenneth Lee <liguozhu@hisilicon.com>, Hao
> Fang <fanghao11@huawei.com>, Zhou Wang <wangzhou1@hisilicon.com>, Zaibo Xu
> <xuzaibo@huawei.com>, Philippe Ombredanne <pombredanne@nexb.com>, Greg
> Kroah-Hartman <gregkh@linuxfoundation.org>, Thomas Gleixner
> <tglx@linutronix.de>, linux-doc@vger.kernel.org,
> linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org,
> iommu@lists.linux-foundation.org, kvm@vger.kernel.org,
> linux-accelerators@lists.ozlabs.org, Lu Baolu <baolu.lu@linux.intel.com>,
> Sanjay Kumar <sanjay.k.kumar@intel.com>
> CC: linuxarm@huawei.com
> Subject: Re: [PATCH 1/7] vfio/sdmdev: Add documents for WarpDrive framework
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> Thunderbird/52.9.1
> Message-ID: <56f5f66d-f6d9-f4fa-40ca-e4a8bad170c1@infradead.org>
>
> Hi,
>
> On 09/02/2018 05:51 PM, Kenneth Lee wrote:
> > From: Kenneth Lee <liguozhu@hisilicon.com>
> >
> > 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@hisilicon.com>
> > ---
> > 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:
>

Actually, I tried to say it can be defined like this. But people can choose
other implementation with the same kernel API.

I will say it explicitly in the future version. Thank you.

>
> > + ::
> > + 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: ::
>

Err, the "with..." clause belong to the following "The referred process
space...".

> > +
> > + 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

--
-Kenneth(Hisilicon)

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