netdev - Re: [PATCH net-next] xsk: introduce xsk_dma

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Date:   Tue, 25 Apr 2023 10:11:42 +0800
From:   Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To:     Alexander Lobakin <aleksander.lobakin@...el.com>
Cc:     <netdev@...r.kernel.org>,
        Björn Töpel <bjorn@...nel.org>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        <bpf@...r.kernel.org>, <virtualization@...ts.linux-foundation.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Jens Axboe <axboe@...nel.dk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH net-next] xsk: introduce xsk_dma_ops

On Mon, 24 Apr 2023 17:28:01 +0200, Alexander Lobakin <aleksander.lobakin@...el.com> wrote:
> From: Jakub Kicinski <kuba@...nel.org>
> 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?


Yes

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

Thanks.


>
> Thanks,
> Olek