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From: "Christian König" <christian.koenig@amd.com>
To: Christoph Hellwig <hch@infradead.org>, Jason Gunthorpe <jgg@ziepe.ca>
Cc: David1.Zhou@amd.com, intel-gfx@lists.freedesktop.org,
	dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org,
	Logan Gunthorpe <logang@deltatee.com>,
	linux-media@vger.kernel.org
Subject: Re: [Intel-gfx] [PATCH 1/6] lib/scatterlist: add sg_set_dma_addr() function
Date: Fri, 13 Mar 2020 14:33:37 +0100	[thread overview]
Message-ID: <0beef7ca-dd77-b442-5f45-f3a496189731@amd.com> (raw)
In-Reply-To: <20200313112139.GA4913@infradead.org>

Am 13.03.20 um 12:21 schrieb Christoph Hellwig:
> On Thu, Mar 12, 2020 at 11:19:28AM -0300, Jason Gunthorpe wrote:
>> The non-page scatterlist is also a big concern for RDMA as we have
>> drivers that want the page list, so even if we did as this series
>> contemplates I'd have still have to split the drivers and create the
>> notion of a dma-only SGL.
> The drivers I looked at want a list of IOVA address, aligned to the
> device "page size".  What other data do drivers want?

Well for GPUs I have the requirement that those IOVA addresses allow 
random access.

That's the reason why we currently convert the sg_table into a linear 
arrays of addresses and pages. To solve that keeping the length in 
separate optional array would be ideal for us.

But this is so a special use case that I'm not sure if we want to 
support this in the common framework or not.

> Execept for the software protocol stack drivers, which of couse need pages for the
> stack futher down.

Yes completely agree.

For the GPUs I will propose a patch to stop copying the page from the 
sg_table over into our linear arrays and see if anybody starts to scream.

I don't think so, but probably better to double check.

Thanks,
Christian.

>
>> I haven't used bio_vecs before, do they support chaining like SGL so
>> they can be very big? RDMA dma maps gigabytes of memory
> bio_vecs itself don't have the chaining, but the bios build around them
> do.  But each entry can map a huge pile.  If needed we could use the
> same chaining scheme we use for scatterlists for bio_vecs as well, but
> lets see if we really end up needing that.
>
>> So I'm guessing the path forward is something like
>>
>>   - Add some generic dma_sg data structure and helper
>>   - Add dma mapping code to go from pages to dma_sg
> That has been on my todo list for a while.  All the DMA consolidatation
> is to prepare for that and we're finally getting close.

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  reply	other threads:[~2020-03-13 13:33 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-11 13:51 [Intel-gfx] P2P for DMA-buf Christian König
2020-03-11 13:51 ` [Intel-gfx] [PATCH 1/6] lib/scatterlist: add sg_set_dma_addr() function Christian König
2020-03-11 15:28   ` Christoph Hellwig
2020-03-12 10:14     ` Christian König
2020-03-12 10:19       ` Christoph Hellwig
2020-03-12 10:31         ` Christian König
2020-03-12 10:47           ` Christoph Hellwig
2020-03-12 11:02             ` Christian König
     [not found]             ` <20200312141928.GK31668@ziepe.ca>
2020-03-12 15:39               ` Christian König
2020-03-12 16:13               ` Logan Gunthorpe
2020-03-13 11:21               ` Christoph Hellwig
2020-03-13 13:33                 ` Christian König [this message]
     [not found]                 ` <20200313121742.GZ31668@ziepe.ca>
2020-03-16  8:56                   ` Christoph Hellwig
2020-03-16  9:41                     ` Christian König
2020-03-16  9:52                       ` Christoph Hellwig
2020-03-11 13:51 ` [Intel-gfx] [PATCH 2/6] dma-buf: add peer2peer flag Christian König
2020-03-11 13:51 ` [Intel-gfx] [PATCH 3/6] drm/amdgpu: note that we can handle peer2peer DMA-buf Christian König
2020-03-11 13:51 ` [Intel-gfx] [PATCH 4/6] drm/amdgpu: add checks if DMA-buf P2P is supported Christian König
     [not found]   ` <20200311140415.GB31668@ziepe.ca>
2020-03-11 14:33     ` Christian König
     [not found]       ` <20200311143835.GD31668@ziepe.ca>
2020-03-11 14:43         ` Christian König
2020-03-11 13:51 ` [Intel-gfx] [PATCH 5/6] drm/amdgpu: add support for exporting VRAM using DMA-buf v2 Christian König
2020-03-11 15:08   ` Alex Deucher
2020-03-11 13:51 ` [Intel-gfx] [PATCH 6/6] drm/amdgpu: improve amdgpu_gem_info debugfs file Christian König
2020-03-11 18:09 ` [Intel-gfx] ✗ Fi.CI.CHECKPATCH: warning for series starting with [1/6] lib/scatterlist: add sg_set_dma_addr() function Patchwork
2020-03-11 18:34 ` [Intel-gfx] ✗ Fi.CI.BAT: failure " Patchwork

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