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From: "Christian König" <christian.koenig@amd.com>
To: Jason Gunthorpe <jgg@ziepe.ca>, Daniel Vetter <daniel@ffwll.ch>
Cc: Leon Romanovsky <leon@kernel.org>,
	"linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
	"dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>,
	Doug Ledford <dledford@redhat.com>,
	"Vetter, Daniel" <daniel.vetter@intel.com>,
	"Xiong, Jianxin" <jianxin.xiong@intel.com>
Subject: Re: [RFC PATCH v2 0/3] RDMA: add dma-buf support
Date: Fri, 3 Jul 2020 15:21:08 +0200	[thread overview]
Message-ID: <f2ec5c61-a553-39b5-29e1-568dae9ca2cd@amd.com> (raw)
In-Reply-To: <20200703131445.GU25301@ziepe.ca>

Am 03.07.20 um 15:14 schrieb Jason Gunthorpe:
> On Fri, Jul 03, 2020 at 02:52:03PM +0200, Daniel Vetter wrote:
>
>> So maybe I'm just totally confused about the rdma model. I thought:
>> - you bind a pile of memory for various transactions, that might
>> happen whenever. Kernel driver doesn't have much if any insight into
>> when memory isn't needed anymore. I think in the rdma world that's
>> called registering memory, but not sure.
> Sure, but once registered the memory is able to be used at any moment with
> no visibilty from the kernel.
>
> Unlike GPU the transactions that trigger memory access do not go
> through the kernel - so there is no ability to interrupt a command
> flow and fiddle with mappings.

This is the same for GPUs with user space queues as well.

But we can still say for a process if that this process is using a 
DMA-buf which is moved out and so can't run any more unless the DMA-buf 
is accessible again.

In other words you somehow need to make sure that the hardware is not 
accessing a piece of memory any more when you want to move it.

Christian.

>
> Jason


  reply	other threads:[~2020-07-03 13:21 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-29 17:31 [RFC PATCH v2 0/3] RDMA: add dma-buf support Jianxin Xiong
2020-06-29 17:31 ` [RFC PATCH v2 1/3] RDMA/umem: Support importing dma-buf as user memory region Jianxin Xiong
2020-06-30 19:04   ` Xiong, Jianxin
2020-06-29 17:31 ` [RFC PATCH v2 2/3] RDMA/core: Expand the driver method 'reg_user_mr' to support dma-buf Jianxin Xiong
2020-06-30 19:04   ` Xiong, Jianxin
2020-06-29 17:31 ` [RFC PATCH v2 3/3] RDMA/uverbs: Add uverbs command for dma-buf based MR registration Jianxin Xiong
2020-06-30 19:05   ` Xiong, Jianxin
2020-06-29 18:51 ` [RFC PATCH v2 0/3] RDMA: add dma-buf support Jason Gunthorpe
2020-06-30 17:21   ` Xiong, Jianxin
2020-06-30 17:34     ` Jason Gunthorpe
2020-06-30 18:46       ` Xiong, Jianxin
2020-06-30 19:17         ` Jason Gunthorpe
2020-06-30 20:08           ` Xiong, Jianxin
2020-07-02 12:27             ` Jason Gunthorpe
2020-07-01  9:03         ` Christian König
2020-07-01 12:07           ` Daniel Vetter
2020-07-01 12:14             ` Daniel Vetter
2020-07-01 12:39           ` Jason Gunthorpe
2020-07-01 12:55             ` Christian König
2020-07-01 15:42               ` Daniel Vetter
2020-07-01 17:15                 ` Jason Gunthorpe
2020-07-02 13:10                   ` Daniel Vetter
2020-07-02 13:29                     ` Jason Gunthorpe
2020-07-02 14:50                       ` Christian König
2020-07-02 18:15                         ` Daniel Vetter
2020-07-03 12:03                           ` Jason Gunthorpe
2020-07-03 12:52                             ` Daniel Vetter
2020-07-03 13:14                               ` Jason Gunthorpe
2020-07-03 13:21                                 ` Christian König [this message]
2020-07-07 21:58                                   ` Xiong, Jianxin
2020-07-08  9:38                                     ` Christian König
2020-07-08  9:49                                       ` Daniel Vetter
2020-07-08 14:20                                         ` Christian König
2020-07-08 14:33                                           ` Alex Deucher
2020-06-30 18:56 ` Xiong, Jianxin

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