[RFC PATCH 0/3] Propose new struct drm_mem_region
Brian Welty
brian.welty at intel.com
Wed Jul 31 01:19:50 UTC 2019
On 7/30/2019 2:34 AM, Daniel Vetter wrote:
> On Tue, Jul 30, 2019 at 08:45:57AM +0000, Koenig, Christian wrote:
>> Yeah, that looks like a good start. Just a couple of random design
>> comments/requirements.
>>
>> First of all please restructure the changes so that you more or less
>> have the following:
>> 1. Adding of the new structures and functionality without any change to
>> existing code.
>> 2. Replacing the existing functionality in TTM and all of its drivers.
>> 3. Replacing the existing functionality in i915.
>>
>> This should make it much easier to review the new functionality when it
>> is not mixed with existing TTM stuff.
Sure, understood. But I hope it's fair that I wouldn't be updating all
drivers in an RFC series until there is a bit of clarity/agreement on any
path forward. But I can include amdgpu patch next time.
>>
>>
>> Second please completely drop the concept of gpu_offset or start of the
>> memory region like here:
>>> drm_printf(p, " gpu_offset: 0x%08llX\n", man->region.start);
>> At least on AMD hardware we have the following address spaces which are
>> sometimes even partially overlapping: VM, MC, SYSTEM, FB, AGP, XGMI, bus
>> addresses and physical addresses.
>>
>> Pushing a concept of a general GPU address space into the memory
>> management was a rather bad design mistake in TTM and we should not
>> repeat that here.
>>
>> A region should only consists of a size in bytes and (internal to the
>> region manager) allocations in that region.
Got it. I was trying to include fields that seemed relevant to a base
structure and could then optionally be leveraged at the choice of device
driver. But I see your point.
>>
>>
>> Third please don't use any CPU or architecture specific types in any
>> data structures:
>>> +struct drm_mem_region {
>>> + resource_size_t start; /* within GPU physical address space */
>>> + resource_size_t io_start; /* BAR address (CPU accessible) */
>>> + resource_size_t size;
>>
>> I knew that resource_size is mostly 64bit on modern architectures, but
>> dGPUs are completely separate to the architecture and we always need
>> 64bits here at least for AMD hardware.
>>
>> So this should either be always uint64_t, or something like
>> gpu_resource_size which depends on what the compiled in drivers require
>> if we really need that.
>>
>> And by the way: Please always use bytes for things like sizes and not
>> number of pages, cause page size is again CPU/architecture specific and
>> GPU drivers don't necessary care about that.
Makes sense, will fix.
Hmm, I did hope that at least the DRM cgroup controller could leverage
struct page_counter. It encapsulates nicely much of the fields for
managing a memory limit. But well, this is off topic....
>>
>>
>> And here also a few direct comments on the code:
>>> + union {
>>> + struct drm_mm *mm;
>>> + /* FIXME (for i915): struct drm_buddy_mm *buddy_mm; */
>>> + void *priv;
>>> + };
>> Maybe just always use void *mm here.
>
> I'd say lets drop this outright, and handle private data by embedding this
> structure in the right place. That's how we handle everything in drm now
> as much as possible, and it's so much cleaner. I think ttm still loves
> priv pointers a bit too much in some places.
Okay, I'll drop it until I might be able to prove this might be useful later.
>
>>> + spinlock_t move_lock;
>>> + struct dma_fence *move;
>>
>> That is TTM specific and I'm not sure if we want it in the common memory
>> management handling.
>>
>> If we want that here we should probably replace the lock with some rcu
>> and atomic fence pointer exchange first.
>
> Yeah not sure we want any of these details in this shared structure
> either.
>
Thanks for the feedback. I can remove it too.
I was unsure if might be a case for having it in future.
Well, struct drm_mem_region will be quite small then if it only has a
size and type field.
Hardly seems worth introducing a new structure if these are the only fields.
I know we thought it might benefit cgroups controller, but I still hope to
find earlier purpose it could serve.
-Brian
[snip]
>>
>> 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.
>
> I'm not sure how much of all that we really want in a drm_mem_region ...
> Otherwise we just reimplement the same midlayer we have already, but with
> a drm_ instead of ttm_ prefix. And that seems a bit silly.
> -Daniel
>
>>>
>>> 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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