From: "Christian König" <christian.koenig@amd.com>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.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: Wed, 25 Aug 2021 15:51:14 +0200 [thread overview]
Message-ID: <9c9ebc3b-44d0-0a81-04cc-d500e7f6da8d@amd.com> (raw)
In-Reply-To: <20210825123802.GD1721383@nvidia.com>
Am 25.08.21 um 14:38 schrieb Jason Gunthorpe:
> On Wed, Aug 25, 2021 at 02:27:08PM +0200, Christian König wrote:
>> Am 25.08.21 um 14:18 schrieb Jason Gunthorpe:
>>> On Wed, Aug 25, 2021 at 08:17:51AM +0200, Christian König wrote:
>>>
>>>> The only real option where you could do P2P with buffer pinning are those
>>>> compute boards where we know that everything is always accessible to
>>>> everybody and we will never need to migrate anything. But even then you want
>>>> some mechanism like cgroups to take care of limiting this. Otherwise any
>>>> runaway process can bring down your whole system.
>>> Why? It is not the pin that is the problem, it was allocating GPU
>>> dedicated memory in the first place. pinning it just changes the
>>> sequence to free it. No different than CPU memory.
>> Pinning makes the memory un-evictable.
>>
>> In other words as long as we don't pin anything we can support as many
>> processes as we want until we run out of swap space. Swapping sucks badly
>> because your applications become pretty much unuseable, but you can easily
>> recover from it by killing some process.
>>
>> With pinning on the other hand somebody sooner or later receives an -ENOMEM
>> or -ENOSPC and there is no guarantee that this goes to the right process.
> It is not really different - you have the same failure mode once the
> system runs out of swap.
>
> This is really the kernel side trying to push a policy to the user
> side that the user side doesn't want..
But which is still the right thing to do as far as I can see. See
userspace also doesn't want proper process isolation since it takes
extra time.
Kernel development is driven by exposing the hardware functionality in a
save and manageable manner to userspace, and not by fulfilling userspace
requirements.
This is very important cause you otherwise you create a specialized
system and not a general purpose kernel.
> Dedicated systems are a significant use case here and should be
> supported, even if the same solution wouldn't be applicable to someone
> running a desktop.
And exactly that approach is not acceptable.
Christian.
>
> Jason
next prev parent reply other threads:[~2021-08-25 13:51 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 [this message]
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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