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From: Paul Cercueil <email@example.com> To: Pavel Begunkov <firstname.lastname@example.org>, Jonathan Lemon <email@example.com> Cc: "Jonathan Cameron" <firstname.lastname@example.org>, "Sumit Semwal" <email@example.com>, "Christian König" <firstname.lastname@example.org>, "Christoph Hellwig" <email@example.com>, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, "Michael Hennerich" <Michael.Hennerich@analog.com>, "Alexandru Ardelean" <firstname.lastname@example.org> Subject: Re: IIO, dmabuf, io_uring Date: Mon, 16 Aug 2021 11:20:25 +0200 [thread overview] Message-ID: <1YDXXQ.FDQ4R2DPJ42F@crapouillou.net> (raw) In-Reply-To: <email@example.com> Hi, Le ven., août 13 2021 at 18:20:19 +0100, Pavel Begunkov <firstname.lastname@example.org> a écrit : > Hi Paul, > > On 8/13/21 12:41 PM, Paul Cercueil wrote: >> Hi, >> >> A few months ago we (ADI) tried to upstream the interface we use >> with our high-speed ADCs and DACs. It is a system with custom ioctls >> on the iio device node to dequeue and enqueue buffers (allocated >> with dma_alloc_coherent), that can then be mmap'd by userspace >> applications. Anyway, it was ultimately denied entry ; this API >> was okay in ~2014 when it was designed but it feels like >> re-inventing the wheel in 2021. >> >> Back to the drawing table, and we'd like to design something that >> we can actually upstream. This high-speed interface looks awfully >> similar to DMABUF, so we may try to implement a DMABUF interface for >> IIO, unless someone has a better idea. >> >> Our first usecase is, we want userspace applications to be able to >> dequeue buffers of samples (from ADCs), and/or enqueue buffers of >> samples (for DACs), and to be able to manipulate them (mmapped >> buffers). With a DMABUF interface, I guess the userspace application >> would dequeue a dma buffer from the driver, mmap it, read/write the >> data, unmap it, then enqueue it to the IIO driver again so that it >> can be disposed of. Does that sound sane? >> >> Our second usecase is - and that's where things get tricky - to be >> able to stream the samples to another computer for processing, over >> Ethernet or USB. Our typical setup is a high-speed ADC/DAC on a dev >> board with a FPGA and a weak soft-core or low-power CPU; processing >> the data in-situ is not an option. Copying the data from one buffer >> to another is not an option either (way too slow), so we absolutely >> want zero-copy. >> >> Usual userspace zero-copy techniques (vmsplice+splice, MSG_ZEROCOPY >> etc) don't really work with mmapped kernel buffers allocated for DMA >>  and/or have a huge overhead, so the way I see it, we would also >> need DMABUF support in both the Ethernet stack and USB (functionfs) >> stack. However, as far as I understood, DMABUF is mostly a DRM/V4L2 >> thing, so I am really not sure we have the right idea here. >> >> And finally, there is the new kid in town, io_uring. I am not very >> literate about the topic, but it does not seem to be able to handle >> DMA buffers (yet?). The idea that we could dequeue a buffer of >> samples from the IIO device and send it over the network in one >> single syscall is appealing, though. > > You might be interested to look up zctap, previously a.k.a netgpu. CCing Jonathan (Lemon) then. Jonathan: Am I right that zctap supports importing/exporting dmabufs? Because that would solve half of my problem. Cheers, -Paul > For io_uring, it's work in progress as well. > >> >> Any thoughts? Feedback would be greatly appreciated. >> >> Cheers, >> -Paul >> >> : >> https://email@example.com/T/#m6b853addb77959c55e078fbb06828db33d4bf3d7 >> : >> https://newbedev.com/zero-copy-user-space-tcp-send-of-dma-mmap-coherent-mapped-memory > > -- > Pavel Begunkov
next prev parent reply other threads:[~2021-08-16 9:20 UTC|newest] Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-08-13 11:41 IIO, dmabuf, io_uring Paul Cercueil 2021-08-13 17:20 ` Pavel Begunkov 2021-08-16 9:20 ` Paul Cercueil [this message] 2021-08-14 7:30 ` Christoph Hellwig 2021-08-16 9:27 ` Paul Cercueil 2021-08-16 15:01 ` [Linaro-mm-sig] " Daniel Vetter 2021-08-15 18:02 ` Christian König
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