From: Daniel Vetter <daniel@ffwll.ch>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: "Mina Almasry" <almasrymina@google.com>,
"Christoph Hellwig" <hch@infradead.org>,
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Subject: Re: [RFC PATCH net-next v8 02/14] net: page_pool: create hooks for custom page providers
Date: Tue, 7 May 2024 19:19:46 +0200 [thread overview]
Message-ID: <ZjpisrsAZdqTXuLT@phenom.ffwll.local> (raw)
In-Reply-To: <20240507164838.GG4718@ziepe.ca>
On Tue, May 07, 2024 at 01:48:38PM -0300, Jason Gunthorpe wrote:
> On Tue, May 07, 2024 at 09:42:05AM -0700, Mina Almasry wrote:
>
> > 1. Align with devmem TCP to use udmabuf for your io_uring memory. I
> > think in the past you said it's a uapi you don't link but in the face
> > of this pushback you may want to reconsider.
>
> dmabuf does not force a uapi, you can acquire your pages however you
> want and wrap them up in a dmabuf. No uapi at all.
>
> The point is that dmabuf already provides ops that do basically what
> is needed here. We don't need ops calling ops just because dmabuf's
> ops are not understsood or not perfect. Fixup dmabuf.
>
> If io_uring wants to take its existing memory pre-registration it can
> wrap that in a dmbauf, and somehow pass it to the netstack. Userspace
> doesn't need to know a dmabuf is being used in the background.
So roughly the current dma-buf design considerations for the users of the
dma-api interfaces:
- It's a memory buffer of fixed length.
- Either that memory is permanently nailed into place with dma_buf_pin
(and if we add more users than just drm display then we should probably
figure out the mlock account question for these). For locking hierarchy
dma_buf_pin uses dma_resv_lock which nests within mmap_sem/vma locks but
outside of any reclaim/alloc contexts.
- Or the memory is more dynamic, in which case case you need to be able to
dma_resv_lock when you need the memory and make a promise (as a
dma_fence) that you'll release the memory within finite time and without
any further allocations once you've unlocked the dma_buf (because
dma_fence is in GFP_NORECLAIM). That promise can be waiting for memory
access to finish, but it can also be a pte invalidate+tlb flush, or some
kind of preemption, or whatever your hw can do really.
Also, if you do this dynamic model and need to atomically reserve more
than one dma_buf, you get to do the wait/wound mutex dance, but that's
really just a bunch of funny looking error handling code and not really
impacting the overall design or locking hierarchy.
Everything else we can adjust, but I think the above three are not really
changeable or dma-buf becomes unuseable for gpu drivers.
Note that exporters of dma-buf can pretty much do whatever they feel like,
including rejecting all the generic interfaces/ops, because we also use
dma-buf as userspace handles for some really special memory.
-Sima
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
next prev parent reply other threads:[~2024-05-07 17:19 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-03 0:20 [RFC PATCH net-next v8 00/14] Device Memory TCP Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 01/14] queue_api: define queue api Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 02/14] net: page_pool: create hooks for custom page providers Mina Almasry
2024-05-01 7:54 ` Christoph Hellwig
2024-05-03 20:10 ` Mina Almasry
2024-05-06 12:04 ` Christoph Hellwig
2024-05-07 16:05 ` Pavel Begunkov
2024-05-07 16:18 ` Jason Gunthorpe
2024-05-07 16:23 ` Christoph Hellwig
2024-05-07 16:42 ` Mina Almasry
2024-05-07 16:48 ` Jason Gunthorpe
2024-05-07 17:19 ` Daniel Vetter [this message]
2024-05-07 17:25 ` Pavel Begunkov
2024-05-07 17:56 ` Jason Gunthorpe
2024-05-07 19:35 ` Pavel Begunkov
2024-05-07 23:32 ` Jason Gunthorpe
2024-05-08 7:16 ` Daniel Vetter
2024-05-08 11:35 ` Pavel Begunkov
2024-05-08 15:34 ` Daniel Vetter
2024-05-08 15:51 ` Christoph Hellwig
2024-05-08 17:02 ` Pavel Begunkov
2024-05-09 4:49 ` Christoph Hellwig
2024-05-08 11:30 ` Pavel Begunkov
2024-05-08 14:25 ` Jason Gunthorpe
2024-05-08 15:44 ` Pavel Begunkov
2024-05-08 15:58 ` Jason Gunthorpe
2024-05-08 16:13 ` Pavel Begunkov
2024-05-07 17:17 ` Pavel Begunkov
2024-05-07 16:55 ` Pavel Begunkov
2024-05-07 17:15 ` Mina Almasry
2024-05-07 17:34 ` Pavel Begunkov
2024-04-03 0:20 ` [RFC PATCH net-next v8 03/14] net: netdev netlink api to bind dma-buf to a net device Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 04/14] netdev: support binding dma-buf to netdevice Mina Almasry
2024-04-24 17:35 ` David Wei
2024-04-24 22:11 ` Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 05/14] netdev: netdevice devmem allocator Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 06/14] page_pool: convert to use netmem Mina Almasry
2024-04-03 17:27 ` Simon Horman
2024-04-03 0:20 ` [RFC PATCH net-next v8 07/14] page_pool: devmem support Mina Almasry
2024-04-27 0:17 ` David Wei
2024-04-27 2:11 ` Mina Almasry
2024-04-30 13:31 ` Pavel Begunkov
2024-04-30 13:45 ` Jens Axboe
2024-04-30 18:29 ` Mina Almasry
2024-04-30 18:55 ` Jens Axboe
2024-04-30 19:19 ` Mina Almasry
2024-05-01 13:58 ` Jesper Dangaard Brouer
2024-05-01 7:55 ` Christoph Hellwig
2024-05-06 0:29 ` David Wei
2024-04-03 0:20 ` [RFC PATCH net-next v8 08/14] memory-provider: dmabuf devmem memory provider Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 09/14] net: support non paged skb frags Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 10/14] net: add support for skbs with unreadable frags Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 11/14] tcp: RX path for devmem TCP Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 12/14] net: add SO_DEVMEM_DONTNEED setsockopt to release RX frags Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 13/14] net: add devmem TCP documentation Mina Almasry
2024-05-03 13:14 ` Bagas Sanjaya
2024-04-03 0:20 ` [RFC PATCH net-next v8 14/14] selftests: add ncdevmem, netcat for devmem TCP Mina Almasry
2024-04-08 15:57 ` Cong Wang
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