[RFC PATCH 0/3] Propose new struct drm_mem_region

Wed Jul 31 08:25:15 UTC 2019

Am 31.07.19 um 10:05 schrieb Daniel Vetter:
> [SNIP]
>>> Okay, I see now I was far off the mark with what I thought TTM_PL_SYSTEM
>>> was.  The discussion helped clear up several bits of confusion on my part.
>>>   From proposed names, I find MAPPED and PINNED slightly confusing.
>>> In terms of backing store description, maybe these are a little better:
>>>     DRM_MEM_SYS_UNTRANSLATED  (TTM_PL_SYSTEM)
>>>     DRM_MEM_SYS_TRANSLATED    (TTM_PL_TT or i915's SYSTEM)
>> That's still not correct. Let me describe what each of the tree stands for:
>>
>> 1. The backing store is a shmem file so the individual pages are
>> swapable by the core OS.
>> 2. The backing store is allocate GPU accessible but not currently in use
>> by the GPU.
>> 3. The backing store is currently in use by the GPU.
>>
>> For i915 all three of those are basically the same and you only need to
>> worry about it much.
> We do pretty much have these three states for i915 gem bo too. Of
> course none have a reasonable upper limit since it's all shared
> memory. The hard limit would be system memory + swap for 1, and only
> system memory for 2 and 3.

Good to know.

>> But for other drivers that's certainly not true and we need this
>> distinction of the backing store of an object.
>>
>> I'm just not sure how we would handle that for cgroups. From experience
>> we certainly want a limit over all 3, but you usually also want to limit
>> 3 alone.
> To avoid lolz against the shrinker I think you also want to limit 2+3.
> Afaiui ttm does that with the global limit, to avoid driving the
> system against the wall.

Yes, exactly. But I think you only need that when 2+3 are not backed by 
pinning shmem. E.g. for i915 I'm not sure you want this limitation.

> [SNIP]
>> #1 and #2 in my example above should probably not be configured by the
>> driver itself.
>>
>> And yes seeing those as special for state handling sounds like the
>> correct approach to me.
> Do we have any hw that wants custom versions of 3?

I can't think of any. If a driver needs something special for 3 then 
that should be domain VRAM or domain PRIV.

As far as I can see with the proposed separation we can even handle AGP.

> The only hw designs
> I know of either have one shared translation table (but only one per
> device, so having just 1 domain is good enough). Or TT mappings are in
> the per-process pagetables, and then you're defacto unlimited (and
> again one domain is good enough). So roughly:
>
> - 1&2 global accross all drivers. 1 and 2 are disjoint (i.e. a bo is
> only account to one of them, never both).
> - 3 would be a subgroup of 2, and per device. A bo in group 3 is also
> always in group 2.

Yes, that sounds like a good description certainly like the right why to 
see it.

> For VRAM and VRAM-similar things (like stolen system memory, or if you
> have VRAM that's somehow split up like with a dual gpu perhaps) I
> agree the driver needs to register that. And we just have some
> standard flags indicating that "this is kinda like VRAM".

Yeah, agree totally as well.

Christian.

> -Daniel
>
>> Regards,
>> Christian.
>>
>>>>>>> TTM was clearly missing that resulting in a whole bunch of extra
>>>>>>> handling and rather complicated handling.
>>>>>>>
>>>>>>>> +#define DRM_MEM_SYSTEM     0
>>>>>>>> +#define DRM_MEM_STOLEN     1
>>>>>>> I think we need a better naming for that.
>>>>>>>
>>>>>>> STOLEN sounds way to much like stolen VRAM for integrated GPUs, but at
>>>>>>> least for TTM this is the system memory currently GPU accessible.
>>>>>> Yup this is wrong, for i915 we use this as stolen, for ttm it's the gpu
>>>>>> translation table window into system memory. Not the same thing at all.
>>>>> Thought so. The closest I have in mind is GTT, but everything else works
>>>>> as well.
>>>> Would your GPU_MAPPED above work for TT? I think we'll also need
>>>> STOLEN, I'm even hearing noises that there's going to be stolen for
>>>> discrete vram for us ... Also if we expand I guess we need to teach
>>>> ttm to cope with more, or maybe treat the DRM one as some kind of
>>>> sub-flavour.
>>> Daniel, maybe what i915 calls stolen could just be DRM_MEM_RESERVED or
>>> DRM_MEM_PRIV.  Or maybe can argue it falls into UNTRANSLATED type that
>>> I suggested above, I'm not sure.
>>>
>>> -Brian
>>>
>>>
>>>> -Daniel
>>>>
>>>>> Christian.
>>>>>
>>>>>> -Daniel
>>>>>>
>>>>>>> Thanks for looking into that,
>>>>>>> Christian.
>>>>>>>
>>>>>>> Am 30.07.19 um 02:32 schrieb Brian Welty:
>>>>>>>> [ By request, resending to include amd-gfx + intel-gfx.  Since resending,
>>>>>>>>       I fixed the nit with ordering of header includes that Sam noted. ]
>>>>>>>>
>>>>>>>> This RFC series is first implementation of some ideas expressed
>>>>>>>> earlier on dri-devel [1].
>>>>>>>>
>>>>>>>> Some of the goals (open for much debate) are:
>>>>>>>>       - Create common base structure (subclass) for memory regions (patch #1)
>>>>>>>>       - Create common memory region types (patch #2)
>>>>>>>>       - Create common set of memory_region function callbacks (based on
>>>>>>>>         ttm_mem_type_manager_funcs and intel_memory_regions_ops)
>>>>>>>>       - Create common helpers that operate on drm_mem_region to be leveraged
>>>>>>>>         by both TTM drivers and i915, reducing code duplication
>>>>>>>>       - Above might start with refactoring ttm_bo_manager.c as these are
>>>>>>>>         helpers for using drm_mm's range allocator and could be made to
>>>>>>>>         operate on DRM structures instead of TTM ones.
>>>>>>>>       - Larger goal might be to make LRU management of GEM objects common, and
>>>>>>>>         migrate those fields into drm_mem_region and drm_gem_object strucures.
>>>>>>>>
>>>>>>>> Patches 1-2 implement the proposed struct drm_mem_region and adds
>>>>>>>> associated common set of definitions for memory region type.
>>>>>>>>
>>>>>>>> Patch #3 is update to i915 and is based upon another series which is
>>>>>>>> in progress to add vram support to i915 [2].
>>>>>>>>
>>>>>>>> [1] https://lists.freedesktop.org/archives/dri-devel/2019-June/224501.html
>>>>>>>> [2] https://lists.freedesktop.org/archives/intel-gfx/2019-June/203649.html
>>>>>>>>
>>>>>>>> Brian Welty (3):
>>>>>>>>       drm: introduce new struct drm_mem_region
>>>>>>>>       drm: Introduce DRM_MEM defines for specifying type of drm_mem_region
>>>>>>>>       drm/i915: Update intel_memory_region to use nested drm_mem_region
>>>>>>>>
>>>>>>>>      drivers/gpu/drm/i915/gem/i915_gem_object.c    |  2 +-
>>>>>>>>      drivers/gpu/drm/i915/gem/i915_gem_shmem.c     |  2 +-
>>>>>>>>      drivers/gpu/drm/i915/i915_gem_gtt.c           | 10 ++---
>>>>>>>>      drivers/gpu/drm/i915/i915_gpu_error.c         |  2 +-
>>>>>>>>      drivers/gpu/drm/i915/i915_query.c             |  2 +-
>>>>>>>>      drivers/gpu/drm/i915/intel_memory_region.c    | 10 +++--
>>>>>>>>      drivers/gpu/drm/i915/intel_memory_region.h    | 19 +++------
>>>>>>>>      drivers/gpu/drm/i915/intel_region_lmem.c      | 26 ++++++-------
>>>>>>>>      .../drm/i915/selftests/intel_memory_region.c  |  8 ++--
>>>>>>>>      drivers/gpu/drm/ttm/ttm_bo.c                  | 34 +++++++++-------
>>>>>>>>      drivers/gpu/drm/ttm/ttm_bo_manager.c          | 14 +++----
>>>>>>>>      drivers/gpu/drm/ttm/ttm_bo_util.c             | 11 +++---
>>>>>>>>      drivers/gpu/drm/vmwgfx/vmwgfx_gmrid_manager.c |  8 ++--
>>>>>>>>      drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c    |  4 +-
>>>>>>>>      include/drm/drm_mm.h                          | 39 ++++++++++++++++++-
>>>>>>>>      include/drm/ttm/ttm_bo_api.h                  |  2 +-
>>>>>>>>      include/drm/ttm/ttm_bo_driver.h               | 16 ++++----
>>>>>>>>      include/drm/ttm/ttm_placement.h               |  8 ++--
>>>>>>>>      18 files changed, 124 insertions(+), 93 deletions(-)
>>>>>>>>
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