linux-kernel - Re: [PATCH drm-misc-next v3 5/7] drm/gpuvm: add an abstraction for a VM / BO combination

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Date:   Mon, 11 Sep 2023 20:37:44 +0200
From:   Thomas Hellström 
        <thomas.hellstrom@...ux.intel.com>
To:     Danilo Krummrich <dakr@...hat.com>, airlied@...il.com,
        daniel@...ll.ch, matthew.brost@...el.com, sarah.walker@...tec.com,
        donald.robson@...tec.com, boris.brezillon@...labora.com,
        christian.koenig@....com, faith.ekstrand@...labora.com
Cc:     dri-devel@...ts.freedesktop.org, nouveau@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH drm-misc-next v3 5/7] drm/gpuvm: add an abstraction for a
 VM / BO combination


On 9/11/23 19:49, Danilo Krummrich wrote:
> Hi Thomas,
>
> On 9/11/23 19:19, Thomas Hellström wrote:
>> Hi, Danilo
>>
>> On 9/9/23 17:31, Danilo Krummrich wrote:
>>> This patch adds an abstraction layer between the drm_gpuva mappings of
>>> a particular drm_gem_object and this GEM object itself. The abstraction
>>> represents a combination of a drm_gem_object and drm_gpuvm. The
>>> drm_gem_object holds a list of drm_gpuvm_bo structures (the structure
>>> representing this abstraction), while each drm_gpuvm_bo contains 
>>> list of
>>> mappings of this GEM object.
>>>
>>> This has multiple advantages:
>>>
>>> 1) We can use the drm_gpuvm_bo structure to attach it to various lists
>>>     of the drm_gpuvm. This is useful for tracking external and evicted
>>>     objects per VM, which is introduced in subsequent patches.
>>>
>>> 2) Finding mappings of a certain drm_gem_object mapped in a certain
>>>     drm_gpuvm becomes much cheaper.
>>>
>>> 3) Drivers can derive and extend the structure to easily represent
>>>     driver specific states of a BO for a certain GPUVM.
>>>
>>> The idea of this abstraction was taken from amdgpu, hence the credit 
>>> for
>>> this idea goes to the developers of amdgpu.
>>>
>>> Cc: Christian König <christian.koenig@....com>
>>> Signed-off-by: Danilo Krummrich <dakr@...hat.com>
>>
>> Did you consider having the drivers embed the struct drm_gpuvm_bo in 
>> their own bo definition? I figure that would mean using the gem bo's 
>> refcounting and providing a helper to call from the driver's bo 
>> release. Looks like that could potentially save a lot of code? Or is 
>> there something that won't work with that approach?
>
> There are drm_gpuvm_ops::vm_bo_alloc and drm_gpuvm_ops::vm_bo_free 
> callback for drivers to register for that purpose.

Ah OK. Thanks, I'll take a deeper look.

/Thomas


>
> - Danilo
>
>>
>> Thanks,
>>
>> Thomas
>>
>>
>