Re: [RFC PATCH 0/7] A General Accelerator Framework, WarpDrive

[Kenneth Lee]

On Fri, Aug 03, 2018 at 03:20:43PM +0100, Alan Cox wrote:
> Date: Fri, 3 Aug 2018 15:20:43 +0100
> From: Alan Cox <gnomes@xxxxxxxxxxxxxxxxxxx>
> To: Jerome Glisse <jglisse@xxxxxxxxxx>
> CC: "Tian, Kevin" <kevin.tian@xxxxxxxxx>, Kenneth Lee
>  <nek.in.cn@xxxxxxxxx>, Hao Fang <fanghao11@xxxxxxxxxx>, Herbert Xu
>  <herbert@xxxxxxxxxxxxxxxxxxx>, "kvm@xxxxxxxxxxxxxxx"
>  <kvm@xxxxxxxxxxxxxxx>, Jonathan Corbet <corbet@xxxxxxx>, Greg
>  Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>, "linux-doc@xxxxxxxxxxxxxxx"
>  <linux-doc@xxxxxxxxxxxxxxx>, "Kumar, Sanjay K" <sanjay.k.kumar@xxxxxxxxx>,
>  "iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx" <iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx>,
>  "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>,
>  "linuxarm@xxxxxxxxxx" <linuxarm@xxxxxxxxxx>, Alex Williamson
>  <alex.williamson@xxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>,
>  "linux-crypto@xxxxxxxxxxxxxxx" <linux-crypto@xxxxxxxxxxxxxxx>, Philippe
>  Ombredanne <pombredanne@xxxxxxxx>, Zaibo Xu <xuzaibo@xxxxxxxxxx>, Kenneth
>  Lee <liguozhu@xxxxxxxxxxxxx>, "David S . Miller" <davem@xxxxxxxxxxxxx>,
>  Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> Subject: Re: [RFC PATCH 0/7] A General Accelerator Framework, WarpDrive
> Organization: Intel Corporation
> X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; x86_64-redhat-linux-gnu)
> Message-ID: <20180803152043.40f88947@alans-desktop>
> 
> > If we are going to have any kind of general purpose accelerator API then
> > > it has to be able to implement things like  
> > 
> > Why is the existing driver model not good enough ? So you want
> > a device with function X you look into /dev/X (for instance
> > for GPU you look in /dev/dri)
> 
> Except when my GPU is in an FPGA in which case it might be somewhere else
> or it's a general purpose accelerator that happens to be usable as a GPU.
> Unusual today in big computer space but you'll find it in
> microcontrollers.
> 
> > Each of those device need a userspace driver and thus this
> > user space driver can easily knows where to look. I do not
> > expect that every application will reimplement those drivers
> > but instead use some kind of library that provide a high
> > level API for each of those devices.
> 
> Think about it from the user level. You have a pipeline of things you
> wish to execute, you need to get the right accelerator combinations and
> they need to fit together to meet system constraints like number of
> IOMMU ids the accelerator supports, where they are connected.
> 
> > Now you have a hierarchy of memory for the CPU (HBM, local
> > node main memory aka you DDR dimm, persistent memory) each
> 
> It's not a heirarchy, it's a graph. There's no fundamental reason two
> accelerators can't be close to two different CPU cores but have shared
> HBM that is far from each processor. There are physical reasons it tends
> to look more like a heirarchy today.
> 
> > Anyway i think finding devices and finding relation between
> > devices and memory is 2 separate problems and as such should
> > be handled separatly.
> 
> At a certain level they are deeply intertwined because you need a common
> API. It's not good if I want a particular accelerator and need to then
> see which API its under on this machine and which interface I have to
> use, and maybe have a mix of FPGA, WarpDrive and Google ASIC interfaces
> all different.
> 
> The job of the kernel is to impose some kind of sanity and unity on this
> lot.
> 
> All of it in the end comes down to
> 
> 'Somehow glue some chunk of memory into my address space and find any
> supporting driver I need'
> 

Agree. This is also our intension on WarpDrive. And it looks VFIO is the best
place to fulfill this requirement.

> plus virtualization of the above.
> 
> That bit's easy - but making it usable is a different story.
> 
> Alan

-- 
			-Kenneth(Hisilicon)

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