[PATCH v5 4/4] drm/amdgpu: track bo memory stats at runtime

[Tvrtko Ursulin]

On 23/10/2024 10:14, Christian König wrote:
> Am 23.10.24 um 09:38 schrieb Tvrtko Ursulin:
>>
>> On 22/10/2024 17:24, Christian König wrote:
>>> Am 22.10.24 um 17:17 schrieb Li, Yunxiang (Teddy):
>>>> [Public]
>>>>
>>>>>> +static uint32_t fold_memtype(uint32_t memtype) {
>>>>> In general please add prefixes to even static functions, e.g. 
>>>>> amdgpu_vm_ or
>>>>> amdgpu_bo_.
>>>>>
>>>>>> +   /* Squash private placements into 'cpu' to keep the legacy 
>>>>>> userspace view.
>>>>> */
>>>>>> +   switch (mem_type) {
>>>>>> +   case TTM_PL_VRAM:
>>>>>> +   case TTM_PL_TT:
>>>>>> +           return memtype
>>>>>> +   default:
>>>>>> +           return TTM_PL_SYSTEM;
>>>>>> +   }
>>>>>> +}
>>>>>> +
>>>>>> +static uint32_t bo_get_memtype(struct amdgpu_bo *bo) {
>>>>> That whole function belongs into amdgpu_bo.c
>>>> Do you mean bo_get_memtype or fold_memtype? I debated whether 
>>>> bo_get_memtype should go into amdgpu_vm.c or amdgpu_bo.c, and since 
>>>> it's using fold_memtype and only useful for memory stats because of 
>>>> folding the private placements I just left them here together with 
>>>> the other mem stats code.
>>>>
>>>> I can move it to amdgpu_bo.c make it return the memtype verbatim and 
>>>> just fold it when I do the accounting.
>>>
>>> I think that folding GDS, GWS and OA into system is also a bug. We 
>>> should really not doing that.
>>>
>>> Just wanted to point out for this round that the code to query the 
>>> current placement from a BO should probably go into amdgpu_bo.c and 
>>> not amdgpu_vm.c
>>>
>>>>
>>>>>> +   struct ttm_resource *res = bo->tbo.resource;
>>>>>> +   const uint32_t domain_to_pl[] = {
>>>>>> +           [ilog2(AMDGPU_GEM_DOMAIN_CPU)]      = TTM_PL_SYSTEM,
>>>>>> +           [ilog2(AMDGPU_GEM_DOMAIN_GTT)]      = TTM_PL_TT,
>>>>>> +           [ilog2(AMDGPU_GEM_DOMAIN_VRAM)]     = TTM_PL_VRAM,
>>>>>> +           [ilog2(AMDGPU_GEM_DOMAIN_GDS)]      = AMDGPU_PL_GDS,
>>>>>> +           [ilog2(AMDGPU_GEM_DOMAIN_GWS)]      = AMDGPU_PL_GWS,
>>>>>> +           [ilog2(AMDGPU_GEM_DOMAIN_OA)]       = AMDGPU_PL_OA,
>>>>>> +           [ilog2(AMDGPU_GEM_DOMAIN_DOORBELL)] =
>>>>> AMDGPU_PL_DOORBELL,
>>>>>> +   };
>>>>>> +   uint32_t domain;
>>>>>> +
>>>>>> +   if (res)
>>>>>> +           return fold_memtype(res->mem_type);
>>>>>> +
>>>>>> +   /*
>>>>>> +    * If no backing store use one of the preferred domain for basic
>>>>>> +    * stats. We take the MSB since that should give a reasonable
>>>>>> +    * view.
>>>>>> +    */
>>>>>> +   BUILD_BUG_ON(TTM_PL_VRAM < TTM_PL_TT || TTM_PL_VRAM <
>>>>> TTM_PL_SYSTEM);
>>>>>> +   domain = fls(bo->preferred_domains & AMDGPU_GEM_DOMAIN_MASK);
>>>>>> +   if (drm_WARN_ON_ONCE(&adev->ddev,
>>>>>> +                        domain == 0 || --domain >= 
>>>>>> ARRAY_SIZE(domain_to_pl)))
>>>>> It's perfectly legal to create a BO without a placement. That one 
>>>>> just won't have a
>>>>> backing store.
>>>>>
>>>> This is lifted from the previous change I'm rebasing onto. I think 
>>>> what it’s trying to do is if the BO doesn't have a placement, use 
>>>> the "biggest" (VRAM > TT > SYSTEM) preferred placement for the 
>>>> purpose of accounting. Previously we just ignore BOs that doesn't 
>>>> have a placement. I guess there's argument for going with either 
>>>> approaches.
>>>
>>> I was not arguing, I'm simply pointing out a bug. It's perfectly 
>>> valid for bo->preferred_domains to be 0.
>>>
>>> So the following WARN_ON() that no bit is set is incorrect.
>>>
>>>>
>>>>>> +           return 0;
>>>>>> +   return fold_memtype(domain_to_pl[domain])
>>>>> That would need specular execution mitigation if I'm not completely 
>>>>> mistaken.
>>>>>
>>>>> Better use a switch/case statement.
>>>>>
>>>> Do you mean change the array indexing to a switch statement?
>>>
>>> Yes.
>>
>> Did you mean array_index_nospec?
> 
> Yes.
> 
>> Domain is not a direct userspace input and is calculated from the mask 
>> which sanitized to allowed values prior to this call. So I *think* 
>> switch is an overkill but don't mind it either. Just commenting FWIW.
> 
> I missed that the mask is applied.
> 
> Thinking more about it I'm not sure if we should do this conversion in 
> the first place. IIRC Tvrtko you once suggested a patch which switched a 
> bunch of code to use the TTM placement instead of the UAPI flags.

Maybe 8fb0efb10184 ("drm/amdgpu: Reduce mem_type to domain double 
indirection") is what are you thinking of?

> Going more into this direction I think when we want to look at the 
> current placement we should probably also use the TTM PL enumeration 
> directly.

It does this already. The placement flags are just to "invent" a TTM PL 
enum when bo->tbo.resource == NULL.

         if (!res) {
                 /*
                  * If no backing store use one of the preferred domain 
for basic
                  * stats. We take the MSB since that should give a 
reasonable
                  * view.
                  */
                 BUILD_BUG_ON(TTM_PL_VRAM < TTM_PL_TT ||
                              TTM_PL_VRAM < TTM_PL_SYSTEM);
                 type = fls(bo->preferred_domains & AMDGPU_GEM_DOMAIN_MASK);
                 if (!type)
                         return;
                 type--;
                 if (drm_WARN_ON_ONCE(&adev->ddev,
                                      type >= ARRAY_SIZE(domain_to_pl)))
                         return;
                 type = domain_to_pl[type];
         } else {
                 type = res->mem_type;
         }
...
         stats[type].total += size;
         if (drm_gem_object_is_shared_for_memory_stats(obj))
                 stats[type].drm.shared += size;
         else
                 stats[type].drm.private += size;
... etc ...

So all actual stat accounting is based on TTM PL type enum. And then 
later at fdinfo print time:

         for (i = 0; i < TTM_PL_PRIV; i++)
                 drm_print_memory_stats(p,
                                        &stats[i].drm,
                                        DRM_GEM_OBJECT_RESIDENT |
                                        DRM_GEM_OBJECT_PURGEABLE,
                                        pl_name[i]);

Again, based of the same enum. Not sure if you have something other in 
mind or you are happy with that?

Then what Teddy does is IMO only tangential, he just changes when stats 
are collected and not this aspect.

To fold or not the special placements (GWS, GDS & co) is also 
tangential. In my patch I just preserved the legacy behaviour so it can 
easily be tweaked on top.

Regards,

Tvrtko

> 
> Regards,
> Christian.
> 
>>
>> Regards,
>>
>> Tvrtko
>