[PATCH 1/2] Documentation/gpu: Document the situation with unqualified drm-memory-

[Tvrtko Ursulin]

On 21/08/2024 21:47, Alex Deucher wrote:
> On Tue, Aug 13, 2024 at 9:57 AM Tvrtko Ursulin <tursulin at igalia.com> wrote:
>>
>> From: Tvrtko Ursulin <tvrtko.ursulin at igalia.com>
>>
>> Currently it is not well defined what is drm-memory- compared to other
>> categories.
>>
>> In practice the only driver which emits these keys is amdgpu and in them
>> exposes the current resident buffer object memory (including shared).
>>
>> To prevent any confusion, document that drm-memory- is deprecated and an
>> alias for drm-resident-memory-.
>>
>> While at it also clarify that the reserved sub-string 'memory' refers to
>> the memory region component, and also clarify the intended semantics of
>> other memory categories.
>>
>> v2:
>>   * Also mark drm-memory- as deprecated.
>>   * Add some more text describing memory categories. (Alex)
>>
>> v3:
>>   * Semantics of the amdgpu drm-memory is actually as drm-resident.
>>
>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at igalia.com>
>> Cc: Alex Deucher <alexander.deucher at amd.com>
>> Cc: Christian König <christian.keonig at amd.com>
>> Cc: Rob Clark <robdclark at chromium.org>
>> ---
>>   Documentation/gpu/drm-usage-stats.rst | 25 ++++++++++++++++++++++---
>>   1 file changed, 22 insertions(+), 3 deletions(-)
>>
>> diff --git a/Documentation/gpu/drm-usage-stats.rst b/Documentation/gpu/drm-usage-stats.rst
>> index a80f95ca1b2f..ff964c707754 100644
>> --- a/Documentation/gpu/drm-usage-stats.rst
>> +++ b/Documentation/gpu/drm-usage-stats.rst
>> @@ -144,7 +144,9 @@ Memory
>>
>>   Each possible memory type which can be used to store buffer objects by the
>>   GPU in question shall be given a stable and unique name to be returned as the
>> -string here.  The name "memory" is reserved to refer to normal system memory.
>> +string here.
>> +
>> +The region name "memory" is reserved to refer to normal system memory.
>>
>>   Value shall reflect the amount of storage currently consumed by the buffer
>>   objects belong to this client, in the respective memory region.
>> @@ -152,6 +154,9 @@ objects belong to this client, in the respective memory region.
>>   Default unit shall be bytes with optional unit specifiers of 'KiB' or 'MiB'
>>   indicating kibi- or mebi-bytes.
>>
>> +This key is deprecated and is an alias for drm-resident-<region>. Only one of
>> +the two should be present in the output.
>> +
> 
> I'm not sure how best to handle this.  What should amdgpu do?  We have
> customers out in the field using these existing fields and then with
> patch 2, they go away.  Arguably we'd want both for backwards
> compatibility.

Exactly, so it looks you maybe missed that 2/2 is not removing the 
amdgpu "legacy" drm-memory-. It keeps outputting it and also duplicating 
under drm-resident-. This is mentioned in the commit paragraph:

"""
Legacy keys have been preserved, with the outlook of only potentially
removing only the drm-memory- when the time gets right.
"""

Put differently, I don't think 2/2 should break the existing 
tools/parsers. Only if they have hardcoded assumptions about the order 
of keys perhaps?

Regards,

Tvrtko

>>   - drm-shared-<region>: <uint> [KiB|MiB]
>>
>>   The total size of buffers that are shared with another file (e.g., have more
>> @@ -159,20 +164,34 @@ than a single handle).
>>
>>   - drm-total-<region>: <uint> [KiB|MiB]
>>
>> -The total size of buffers that including shared and private memory.
>> +The total size of all created buffers including shared and private memory. The
>> +backing store for the buffers does not have to be currently instantiated to be
>> +counted under this category.
>>
>>   - drm-resident-<region>: <uint> [KiB|MiB]
>>
>> -The total size of buffers that are resident in the specified region.
>> +The total size of buffers that are resident (have their backing store present or
>> +instantiated) in the specified region.
>> +
>> +This is an alias for drm-memory-<region> and only one of the two should be
>> +present in the output.
>>
>>   - drm-purgeable-<region>: <uint> [KiB|MiB]
>>
>>   The total size of buffers that are purgeable.
>>
>> +For example drivers which implement a form of 'madvise' like functionality can
>> +here count buffers which have instantiated backing store, but have been marked
>> +with an equivalent of MADV_DONTNEED.
>> +
>>   - drm-active-<region>: <uint> [KiB|MiB]
>>
>>   The total size of buffers that are active on one or more engines.
>>
>> +One practical example of this can be presence of unsignaled fences in an GEM
>> +buffer reservation object. Therefore the active category is a subset of
>> +resident.
>> +
>>   Implementation Details
>>   ======================
>>
>> --
>> 2.44.0
>>