Re: [Intel-gfx] [PATCH v6 00/20] drm/i915/vm_bind: Add VM_BIND functionality

From: Matthew Auld <matthew.auld@intel.com>
To: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,
	Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>,
	"Zanoni, Paulo R" <paulo.r.zanoni@intel.com>
Cc: "Nikula, Jani" <jani.nikula@intel.com>,
	"intel-gfx@lists.freedesktop.org"
	<intel-gfx@lists.freedesktop.org>,
	"dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>,
	"Hellstrom, Thomas" <thomas.hellstrom@intel.com>,
	"Vetter, Daniel" <daniel.vetter@intel.com>,
	"christian.koenig@amd.com" <christian.koenig@amd.com>
Subject: Re: [Intel-gfx] [PATCH v6 00/20] drm/i915/vm_bind: Add VM_BIND functionality
Date: Thu, 10 Nov 2022 15:05:11 +0000	[thread overview]
Message-ID: <ab3149ab-730b-c3d5-5296-518a9611dd64@intel.com> (raw)
In-Reply-To: <9097e704-841e-673d-4969-73ffc8f9093f@linux.intel.com>

On 10/11/2022 14:47, Tvrtko Ursulin wrote:
> 
> On 10/11/2022 05:49, Niranjana Vishwanathapura wrote:
>> On Wed, Nov 09, 2022 at 04:16:25PM -0800, Zanoni, Paulo R wrote:
>>> On Mon, 2022-11-07 at 00:51 -0800, Niranjana Vishwanathapura wrote:
>>>> DRM_I915_GEM_VM_BIND/UNBIND ioctls allows UMD to bind/unbind GEM
>>>> buffer objects (BOs) or sections of a BOs at specified GPU virtual
>>>> addresses on a specified address space (VM). Multiple mappings can map
>>>> to the same physical pages of an object (aliasing). These mappings 
>>>> (also
>>>> referred to as persistent mappings) will be persistent across multiple
>>>> GPU submissions (execbuf calls) issued by the UMD, without user having
>>>> to provide a list of all required mappings during each submission (as
>>>> required by older execbuf mode).
>>>>
>>>> This patch series support VM_BIND version 1, as described by the param
>>>> I915_PARAM_VM_BIND_VERSION.
>>>>
>>>> Add new execbuf3 ioctl (I915_GEM_EXECBUFFER3) which only works in
>>>> vm_bind mode. The vm_bind mode only works with this new execbuf3 ioctl.
>>>> The new execbuf3 ioctl will not have any execlist support and all the
>>>> legacy support like relocations etc., are removed.
>>>>
>>>> NOTEs:
>>>> * It is based on below VM_BIND design+uapi rfc.
>>>>   Documentation/gpu/rfc/i915_vm_bind.rst
>>>
>>> Hi
>>>
>>> One difference for execbuf3 that I noticed that is not mentioned in the
>>> RFC document is that we now don't have a way to signal
>>> EXEC_OBJECT_WRITE. When looking at the Kernel code, some there are some
>>> pieces that check for this flag:
>>>
>>> - there's code that deals with frontbuffer rendering
>>> - there's code that deals with fences
>>> - there's code that prevents self-modifying batches
>>> - another that seems related to waiting for objects
>>>
>>> Are there any new rules regarding frontbuffer rendering when we use
>>> execbuf3? Any other behavior changes related to the other places that
>>> we should expect when using execbuf3?
>>>
>>
>> Paulo,
>> Most of the EXEC_OBJECT_WRITE check in execbuf path is related to
>> implicit dependency tracker which execbuf3 does not support. The
>> frontbuffer related updated is the only exception and I don't
>> remember the rationale to not require this on execbuf3.
>>
>> Matt, Tvrtko, Daniel, can you please comment here?
> 
> Does not ring a bell to me. Looking at the code it certainly looks like 
> it would be silently failing to handle it properly.
> 
> I'll let people with more experience in this area answer, but from my 
> point of view, if it is decided that it can be left unsupported, then we 
> probably need a way of failing the ioctl is used against a frontbuffer, 
> or something, instead of having display corruption.

Maybe it's a coincidence but there is:
https://patchwork.freedesktop.org/series/110715/

Which looks relevant. Maarten, any hints here?

> 
> Regards,
> 
> Tvrtko