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Date: Mon, 10 Jun 2024 20:32:16 +0100
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To: Mina Almasry <almasrymina@google.com>,
 =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>, David Wei <dw@davidwei.uk>,
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From: Pavel Begunkov <asml.silence@gmail.com>
In-Reply-To: <CAHS8izNwmXQTLc9VADpushYKyeJ4ZY4G9aV47W2-1St65-tKUg@mail.gmail.com>
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On 6/10/24 16:41, Mina Almasry wrote:
> On Mon, Jun 10, 2024 at 5:38 AM Christian König
> <christian.koenig@amd.com> wrote:
>>
>> Am 10.06.24 um 14:16 schrieb Jason Gunthorpe:
>>> On Mon, Jun 10, 2024 at 02:07:01AM +0100, Pavel Begunkov wrote:
>>>> On 6/10/24 01:37, David Wei wrote:
>>>>> On 2024-06-07 17:52, Jason Gunthorpe wrote:
>>>>>> IMHO it seems to compose poorly if you can only use the io_uring
>>>>>> lifecycle model with io_uring registered memory, and not with DMABUF
>>>>>> memory registered through Mina's mechanism.
>>>>> By this, do you mean io_uring must be exclusively used to use this
>>>>> feature?
>>>>>
>>>>> And you'd rather see the two decoupled, so userspace can register w/ say
>>>>> dmabuf then pass it to io_uring?
>>>> Personally, I have no clue what Jason means. You can just as
>>>> well say that it's poorly composable that write(2) to a disk
>>>> cannot post a completion into a XDP ring, or a netlink socket,
>>>> or io_uring's main completion queue, or name any other API.
>>> There is no reason you shouldn't be able to use your fast io_uring
>>> completion and lifecycle flow with DMABUF backed memory. Those are not
>>> widly different things and there is good reason they should work
>>> together.
>>
>> Well there is the fundamental problem that you can't use io_uring to
>> implement the semantics necessary for a dma_fence.
>>
>> That's why we had to reject the io_uring work on DMA-buf sharing from
>> Google a few years ago.
>>
> 
> Any chance someone can link me to this? io_uring, as far as my
> primitive understanding goes, is not yet very adopted at Google, and
> I'm curious what this effort is.
I'm curious as well, I don't remember it floating anywhere in mailing
lists. The only discussion I recall was about
DRM_IOCTL_SYNCOBJ_TIMELINE_WAIT, but it didn't get through only because
someone pushed for evenfds.

-- 
Pavel Begunkov