linux-kernel - Re: [Linaro-mm-sig] [PATCH v3 1/2] habanalabs: define uAPI to export FD for DMA-BUF

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Message-ID: <d358c740-fd3a-9ecd-7001-676e2cb44ec9@gmail.com>
Date:   Tue, 22 Jun 2021 08:37:15 +0200
From:   Christian König <ckoenig.leichtzumerken@...il.com>
To:     Jason Gunthorpe <jgg@...pe.ca>, Oded Gabbay <oded.gabbay@...il.com>
Cc:     Gal Pressman <galpress@...zon.com>, sleybo@...zon.com,
        linux-rdma <linux-rdma@...r.kernel.org>,
        Oded Gabbay <ogabbay@...nel.org>,
        Christoph Hellwig <hch@....de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Christian König <christian.koenig@....com>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>,
        Doug Ledford <dledford@...hat.com>,
        Tomer Tayar <ttayar@...ana.ai>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Alex Deucher <alexander.deucher@....com>,
        Leon Romanovsky <leonro@...dia.com>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@...r.kernel.org>
Subject: Re: [Linaro-mm-sig] [PATCH v3 1/2] habanalabs: define uAPI to export
 FD for DMA-BUF

Am 22.06.21 um 01:29 schrieb Jason Gunthorpe:
> On Mon, Jun 21, 2021 at 10:24:16PM +0300, Oded Gabbay wrote:
>
>> Another thing I want to emphasize is that we are doing p2p only
>> through the export/import of the FD. We do *not* allow the user to
>> mmap the dma-buf as we do not support direct IO. So there is no access
>> to these pages through the userspace.
> Arguably mmaping the memory is a better choice, and is the direction
> that Logan's series goes in. Here the use of DMABUF was specifically
> designed to allow hitless revokation of the memory, which this isn't
> even using.

The major problem with this approach is that DMA-buf is also used for 
memory which isn't CPU accessible.

That was one of the reasons we didn't even considered using the mapping 
memory approach for GPUs.

Regards,
Christian.

>
> So you are taking the hit of very limited hardware support and reduced
> performance just to squeeze into DMABUF..
>
> Jason
> _______________________________________________
> Linaro-mm-sig mailing list
> Linaro-mm-sig@...ts.linaro.org
> https://lists.linaro.org/mailman/listinfo/linaro-mm-sig

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