linux-kernel - Re: [PATCH v4] Documentation/gpu: VM

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Date:   Thu, 16 Nov 2023 15:02:17 +0100
From:   Danilo Krummrich <dakr@...hat.com>
To:     Thomas Hellström 
        <thomas.hellstrom@...ux.intel.com>,
        Boris Brezillon <boris.brezillon@...labora.com>
Cc:     intel-xe@...ts.freedesktop.org,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Matthew Brost <matthew.brost@...el.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Oak Zeng <oak.zeng@...el.com>, Daniel Vetter <daniel@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Francois Dugast <francois.dugast@...el.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] Documentation/gpu: VM_BIND locking document

On 11/16/23 12:48, Thomas Hellström wrote:

<snip>

>>> +Locks used and locking orders
>>> +=============================
>>> +
>>> +One of the benefits of VM_BIND is that local GEM objects share the
>>> gpu_vm's
>>> +dma_resv object and hence the dma_resv lock. So even with a huge
>>> +number of local GEM objects, only one lock is needed to make the
>>> exec
>>> +sequence atomic.
>>> +
>>> +The following locks and locking orders are used:
>>> +
>>> +* The ``gpu_vm->lock`` (optionally an rwsem). Protects how the
>>> gpu_vm is
>>> +  partitioned into gpu_vmas. It can also protect the gpu_vm's list
>>> of
>>> +  userptr gpu_vmas. With a CPU mm analogy this would correspond to
>>> the
>>> +  mmap_lock.
>>
>> I don't see any drm_gpuvm::lock field in Danilo's latest patchset,
>> so,
>> unless I missed one version, and this lock is actually provided by
>> drm_gpuvm, I would mention this is a driver-specific lock. This
>> comment
>> applies to all the locks you describe here actually (mention which
>> ones
>> are provided by drm_gpuvm, and which ones are driver-specific).
> 
> These will be needed also by gpuvm when implementing userptr vmas, so I
> can mention that drm_gpuvm is currently lacking a userptr
> implementation, so "the locks described below are to be considered
> driver-specific for now"

Since Xe already implements userptr support, are you guys maybe interested
in extending drm_gpuvm accordingly? :-)