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From: Gal Pressman <galpress@amazon.com>
To: Jason Gunthorpe <jgg@ziepe.ca>, John Hubbard <jhubbard@nvidia.com>
Cc: "Christian König" <christian.koenig@amd.com>,
	"Daniel Vetter" <daniel@ffwll.ch>,
	"Sumit Semwal" <sumit.semwal@linaro.org>,
	"Doug Ledford" <dledford@redhat.com>,
	"open list:DMA BUFFER SHARING FRAMEWORK"
	<linux-media@vger.kernel.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	linux-rdma <linux-rdma@vger.kernel.org>,
	"Oded Gabbay" <ogabbay@habana.ai>,
	"Tomer Tayar" <ttayar@habana.ai>,
	"Yossi Leybovich" <sleybo@amazon.com>,
	"Alexander Matushevsky" <matua@amazon.com>,
	"Leon Romanovsky" <leonro@nvidia.com>,
	"Jianxin Xiong" <jianxin.xiong@intel.com>
Subject: Re: [RFC] Make use of non-dynamic dmabuf in RDMA
Date: Wed, 1 Sep 2021 14:20:02 +0300	[thread overview]
Message-ID: <b961e093-b14c-fcdc-e2fc-6ca00cde000c@amazon.com> (raw)
In-Reply-To: <20210824173228.GE543798@ziepe.ca>

On 24/08/2021 20:32, Jason Gunthorpe wrote:
> On Tue, Aug 24, 2021 at 10:27:23AM -0700, John Hubbard wrote:
>> On 8/24/21 2:32 AM, Christian König wrote:
>>> Am 24.08.21 um 11:06 schrieb Gal Pressman:
>>>> On 23/08/2021 13:43, Christian König wrote:
>>>>> Am 21.08.21 um 11:16 schrieb Gal Pressman:
>>>>>> On 20/08/2021 17:32, Jason Gunthorpe wrote:
>>>>>>> On Fri, Aug 20, 2021 at 03:58:33PM +0300, Gal Pressman wrote:
>> ...
>>>>>> IIUC, we're talking about three different exporter "types":
>>>>>> - Dynamic with move_notify (requires ODP)
>>>>>> - Dynamic with revoke_notify
>>>>>> - Static
>>>>>>
>>>>>> Which changes do we need to make the third one work?
>>>>> Basically none at all in the framework.
>>>>>
>>>>> You just need to properly use the dma_buf_pin() function when you start using a
>>>>> buffer (e.g. before you create an attachment) and the dma_buf_unpin() function
>>>>> after you are done with the DMA-buf.
>>>> I replied to your previous mail, but I'll ask again.
>>>> Doesn't the pin operation migrate the memory to host memory?
>>>
>>> Sorry missed your previous reply.
>>>
>>> And yes at least for the amdgpu driver we migrate the memory to host
>>> memory as soon as it is pinned and I would expect that other GPU drivers
>>> do something similar.
>>
>> Well...for many topologies, migrating to host memory will result in a
>> dramatically slower p2p setup. For that reason, some GPU drivers may
>> want to allow pinning of video memory in some situations.
>>
>> Ideally, you've got modern ODP devices and you don't even need to pin.
>> But if not, and you still hope to do high performance p2p between a GPU
>> and a non-ODP Infiniband device, then you would need to leave the pinned
>> memory in vidmem.
>>
>> So I think we don't want to rule out that behavior, right? Or is the
>> thinking more like, "you're lucky that this old non-ODP setup works at
>> all, and we'll make it work by routing through host/cpu memory, but it
>> will be slow"?
> 
> I think it depends on the user, if the user creates memory which is
> permanently located on the GPU then it should be pinnable in this way
> without force migration. But if the memory is inherently migratable
> then it just cannot be pinned in the GPU at all as we can't
> indefinately block migration from happening eg if the CPU touches it
> later or something.

So are we OK with exporters implementing dma_buf_pin() without migrating the memory?
If so, do we still want a move_notify callback for non-dynamic importers? A noop?

  parent reply	other threads:[~2021-09-01 11:20 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-18  7:43 [RFC] Make use of non-dynamic dmabuf in RDMA Gal Pressman
2021-08-18  8:00 ` Christian König
2021-08-18  8:37   ` Gal Pressman
2021-08-18  9:34 ` Daniel Vetter
2021-08-19 23:06   ` Jason Gunthorpe
2021-08-20  7:25     ` Daniel Vetter
2021-08-20 12:33       ` Jason Gunthorpe
2021-08-20 12:58         ` Gal Pressman
2021-08-20 14:32           ` Jason Gunthorpe
2021-08-21  9:16             ` Gal Pressman
2021-08-23 10:43               ` Christian König
2021-08-24  9:06                 ` Gal Pressman
2021-08-24  9:32                   ` Christian König
2021-08-24 17:27                     ` John Hubbard
2021-08-24 17:32                       ` Jason Gunthorpe
2021-08-24 17:35                         ` John Hubbard
2021-08-24 19:15                           ` Dave Airlie
2021-08-24 19:30                             ` Jason Gunthorpe
2021-08-24 19:43                             ` Alex Deucher
2021-08-24 20:00                               ` Xiong, Jianxin
2021-08-25  6:17                         ` Christian König
2021-08-25  6:47                           ` John Hubbard
2021-08-25 12:18                           ` Jason Gunthorpe
2021-08-25 12:27                             ` Christian König
2021-08-25 12:38                               ` Jason Gunthorpe
2021-08-25 13:51                                 ` Christian König
2021-08-25 14:47                                   ` Jason Gunthorpe
2021-08-25 15:14                                     ` Christian König
2021-08-25 15:49                                       ` Jason Gunthorpe
2021-08-25 16:02                                       ` Oded Gabbay
2021-09-01 11:20                         ` Gal Pressman [this message]
2021-09-01 11:24                           ` Christian König
2021-09-02  6:56                             ` Gal Pressman

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