From: Alex Deucher <alexdeucher@gmail.com>
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>,
"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: Tue, 24 Aug 2021 15:43:46 -0400 [thread overview]
Message-ID: <CADnq5_OBt2bQoWzadZ6kR46XU5QMVtzv9aB10CtE49PAotHHPg@mail.gmail.com> (raw)
In-Reply-To: <CAPM=9txd71fisvZ1Es5Fv2mwR2vWfHJarya7oeKOm2aq6tH0HQ@mail.gmail.com>
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
>
> 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.
next prev parent reply other threads:[~2021-08-24 19:43 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 [this message]
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
2021-09-01 11:24 ` Christian König
2021-09-02 6:56 ` Gal Pressman
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