[RFC PATCH 1/7] vfio/spimdev: Add documents for WarpDrive framework

Kenneth Lee nek.in.cn at gmail.com
Wed Aug 8 11:43:05 AEST 2018

在 2018年08月06日 星期一 08:27 下午, Pavel Machek 写道:
> Hi!
>> WarpDrive is a common user space accelerator framework.  Its main component
>> in Kernel is called spimdev, Share Parent IOMMU Mediated Device. It exposes
> spimdev is really unfortunate name. It looks like it has something to do with SPI, but
> it does not.
Yes. Let me change it to Share (IOMMU) Domain MDev, SDMdev:)
>> +++ b/Documentation/warpdrive/warpdrive.rst
>> @@ -0,0 +1,153 @@
>> +Introduction of WarpDrive
>> +=========================
>> +
>> +*WarpDrive* is a general accelerator framework built on top of vfio.
>> +It can be taken as a light weight virtual function, which you can use without
>> +*SR-IOV* like facility and can be shared among multiple processes.
>> +
>> +It can be used as the quick channel for accelerators, network adaptors or
>> +other hardware in user space. It can make some implementation simpler.  E.g.
>> +you can reuse most of the *netdev* driver and just share some ring buffer to
>> +the user space driver for *DPDK* or *ODP*. Or you can combine the RSA
>> +accelerator with the *netdev* in the user space as a Web reversed proxy, etc.
> What is DPDK? ODP?
ODP: https://www.opendataplane.org/

will add the reference in the next RFC
>> +How does it work
>> +================
>> +
>> +*WarpDrive* takes the Hardware Accelerator as a heterogeneous processor which
>> +can share some load for the CPU:
>> +
>> +.. image:: wd.svg
>> +        :alt: This is a .svg image, if your browser cannot show it,
>> +                try to download and view it locally
>> +
>> +So it provides the capability to the user application to:
>> +
>> +1. Send request to the hardware
>> +2. Share memory with the application and other accelerators
>> +
>> +These requirements can be fulfilled by VFIO if the accelerator can serve each
>> +application with a separated Virtual Function. But a *SR-IOV* like VF (we will
>> +call it *HVF* hereinafter) design is too heavy for the accelerator which
>> +service thousands of processes.
> Also "gup" might be worth spelling out.
But I think the reference [1] has explained this.
>> +References
>> +==========
>> +.. [1] Accroding to the comment in in mm/gup.c, The *gup* is only safe within
>> +       a syscall.  Because it can only keep the physical memory in place
>> +       without making sure the VMA will always point to it. Maybe we should
>> +       raise the VM_PINNED patchset (see
>> +       https://lists.gt.net/linux/kernel/1931993) again to solve this probl
> I went through the docs, but I still don't know what it does.
Will refine the doc in next RFC, hope it will help.
> 											Pavel

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