Re: [PATCH net-next] xsk: introduce xsk_dma_ops

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On Mon, 24 Apr 2023 17:28:01 +0200, Alexander Lobakin <aleksander.lobakin@xxxxxxxxx> wrote:
> From: Jakub Kicinski <kuba@xxxxxxxxxx>
> Date: Fri, 21 Apr 2023 06:50:59 -0700
> > On Fri, 21 Apr 2023 15:31:04 +0800 Xuan Zhuo wrote:
> >> I am not particularly familiar with dma-bufs. I want to know if this mechanism
> >> can solve the problem of virtio-net.
> >>
> >> I saw this framework, allowing the driver do something inside the ops of
> >> dma-bufs.
> >>
> >> If so, is it possible to propose a new patch based on dma-bufs?
> >
> > I haven't looked in detail, maybe Olek has? AFAIU you'd need to rework
> Oh no, not me. I suck at dma-bufs, tried to understand them several
> times with no progress :D My knowledge is limited to "ok, if it's
> DMA + userspace, then it's likely dma-buf" :smile_with_tear:
> > uAPI of XSK to allow user to pass in a dma-buf region rather than just
> > a user VA. So it may be a larger effort but architecturally it may be
> > the right solution.
> >
> I'm curious whether this could be done without tons of work. Switching
> Page Pool to dma_alloc_noncoherent() is simpler :D But, as I wrote
> above, we need to extend DMA API first to provide bulk allocations and
> NUMA-aware allocations.
> Can't we provide a shim for back-compat, i.e. if a program passes just a
> user VA, create a dma-buf in the kernel already?


I think so too. If this is the case, will the workload be much smaller? Let me
try it.


> Thanks,
> Olek
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