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From: "Xiong, Jianxin" <jianxin.xiong@intel.com>
To: Alex Deucher <alexdeucher@gmail.com>, Dave Airlie <airlied@gmail.com>
Cc: "John Hubbard" <jhubbard@nvidia.com>,
	"Jason Gunthorpe" <jgg@ziepe.ca>,
	"Christian König" <christian.koenig@amd.com>,
	"Gal Pressman" <galpress@amazon.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>,
	"Gabbay, Oded (Habana)" <ogabbay@habana.ai>,
	"Tayar, Tomer (Habana)" <ttayar@habana.ai>,
	"Yossi Leybovich" <sleybo@amazon.com>,
	"Alexander Matushevsky" <matua@amazon.com>,
	"Leon Romanovsky" <leonro@nvidia.com>
Subject: RE: [RFC] Make use of non-dynamic dmabuf in RDMA
Date: Tue, 24 Aug 2021 20:00:27 +0000	[thread overview]
Message-ID: <DM6PR11MB45482FF79156A2509E4DDDEBE5C59@DM6PR11MB4548.namprd11.prod.outlook.com> (raw)
In-Reply-To: <CADnq5_OBt2bQoWzadZ6kR46XU5QMVtzv9aB10CtE49PAotHHPg@mail.gmail.com>

> -----Original Message-----
> From: Alex Deucher <alexdeucher@gmail.com>
> Sent: Tuesday, August 24, 2021 12:44 PM
> To: Dave Airlie <airlied@gmail.com>
> Cc: John Hubbard <jhubbard@nvidia.com>; Jason Gunthorpe <jgg@ziepe.ca>; Christian König <christian.koenig@amd.com>; Gal Pressman
> <galpress@amazon.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>; Gabbay,
> Oded (Habana) <ogabbay@habana.ai>; Tayar, Tomer (Habana) <ttayar@habana.ai>; Yossi Leybovich <sleybo@amazon.com>; Alexander
> Matushevsky <matua@amazon.com>; Leon Romanovsky <leonro@nvidia.com>; Xiong, Jianxin <jianxin.xiong@intel.com>
> Subject: Re: [RFC] Make use of non-dynamic dmabuf in RDMA
> 
> On Tue, Aug 24, 2021 at 3:16 PM Dave Airlie <airlied@gmail.com> wrote:
> >
> > On Wed, 25 Aug 2021 at 03:36, John Hubbard <jhubbard@nvidia.com> wrote:
> > >
> > > On 8/24/21 10:32 AM, Jason Gunthorpe wrote:
> > > ...
> > > >>> 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.
> > > >
> > >
> > > OK. I just want to avoid creating any API-level assumptions that
> > > dma_buf_pin() necessarily implies or requires migrating to host memory.
> >
> > I'm not sure we should be allowing dma_buf_pin at all on
> > non-migratable memory, what's to stop someone just pinning all the
> > VRAM and making the GPU unuseable?
> 
> In a lot of cases we have GPUs with more VRAM than system memory, but we allow pinning in system memory.
> 
> Alex
> 

In addition, the dma-buf exporter can be a non-GPU device.

Jianxin

> >
> > I understand not considering more than a single user in these
> > situations is enterprise thinking, but I do worry about pinning is
> > always fine type of thinking when things are shared or multi-user.
> >
> > My impression from this is we've designed hardware that didn't
> > consider the problem, and now to let us use that hardware in horrible
> > ways we should just allow it to pin all the things.
> >
> > Dave.

  reply	other threads:[~2021-08-24 20:00 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 [this message]
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
2021-09-01 11:24                           ` Christian König
2021-09-02  6:56                             ` Gal Pressman

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