[RFC PATCH 16/18] drm/amdgpu: Implement SET_PRIORITY GEM op

[Christian König]

Am 25.04.24 um 09:06 schrieb Friedrich Vock:
> On 25.04.24 08:58, Christian König wrote:
>> Am 25.04.24 um 08:46 schrieb Friedrich Vock:
>>> On 25.04.24 08:32, Christian König wrote:
>>>> Am 24.04.24 um 18:57 schrieb Friedrich Vock:
>>>>> Used by userspace to adjust buffer priorities in response to
>>>>> changes in
>>>>> application demand and memory pressure.
>>>>
>>>> Yeah, that was discussed over and over again. One big design criteria
>>>> is that we can't have global priorities from userspace!
>>>>
>>>> The background here is that this can trivially be abused.
>>>>
>>> I see your point when apps are allowed to prioritize themselves above
>>> other apps, and I agree that should probably be disallowed at least for
>>> unprivileged apps.
>>>
>>> Disallowing this is a pretty trivial change though, and I don't really
>>> see the abuse potential in being able to downgrade your own priority?
>>
>> Yeah, I know what you mean and I'm also leaning towards that
>> argumentation. But another good point is also that it doesn't actually
>> help.
>>
>> For example when you have desktop apps fighting with a game, you
>> probably don't want to use static priorities, but rather evict the
>> apps which are inactive and keep the apps which are active in the
>> background.
>>
> Sadly things are not as simple as "evict everything from app 1, keep
> everything from app 2 active". The simplest failure case of this is
> games that already oversubscribe VRAM on their own. Keeping the whole
> app inside VRAM is literally impossible there, and it helps a lot to
> know which buffers the app is most happy with evicting.
>> In other words the priority just tells you which stuff from each app
>> to evict first, but not which app to globally throw out.
>>
> Yeah, but per-buffer priority system could do both of these.

Yeah, but we already have that. See amdgpu_bo_list_entry_cmp() and 
amdgpu_bo_list_create().

This is the per application priority which can be used by userspace to 
give priority to each BO in a submission (or application wide).

The problem is rather that amdgpu/TTM never really made good use of that 
information.

Regards,
Christian.

>
> Regards,
> Friedrich
>
>> Regards,
>> Christian.
>>
>>>
>>> Regards,
>>> Friedrich
>>>
>>>> What we can do is to have per process priorities, but that needs to be
>>>> in the VM subsystem.
>>>>
>>>> That's also the reason why I personally think that the handling
>>>> shouldn't be inside TTM at all.
>>>>
>>>> Regards,
>>>> Christian.
>>>>
>>>>>
>>>>> Signed-off-by: Friedrich Vock <friedrich.vock at gmx.de>
>>>>> ---
>>>>>   drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c | 20 ++++++++++++++++++++
>>>>>   include/uapi/drm/amdgpu_drm.h           |  1 +
>>>>>   2 files changed, 21 insertions(+)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>>>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>>>>> index 5ca13e2e50f50..6107810a9c205 100644
>>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>>>>> @@ -836,8 +836,10 @@ int amdgpu_gem_op_ioctl(struct drm_device *dev,
>>>>> void *data,
>>>>>   {
>>>>>       struct amdgpu_device *adev = drm_to_adev(dev);
>>>>>       struct drm_amdgpu_gem_op *args = data;
>>>>> +    struct ttm_resource_manager *man;
>>>>>       struct drm_gem_object *gobj;
>>>>>       struct amdgpu_vm_bo_base *base;
>>>>> +    struct ttm_operation_ctx ctx;
>>>>>       struct amdgpu_bo *robj;
>>>>>       int r;
>>>>>
>>>>> @@ -851,6 +853,9 @@ int amdgpu_gem_op_ioctl(struct drm_device *dev,
>>>>> void *data,
>>>>>       if (unlikely(r))
>>>>>           goto out;
>>>>>
>>>>> +    memset(&ctx, 0, sizeof(ctx));
>>>>> +    ctx.interruptible = true;
>>>>> +
>>>>>       switch (args->op) {
>>>>>       case AMDGPU_GEM_OP_GET_GEM_CREATE_INFO: {
>>>>>           struct drm_amdgpu_gem_create_in info;
>>>>> @@ -898,6 +903,21 @@ int amdgpu_gem_op_ioctl(struct drm_device *dev,
>>>>> void *data,
>>>>>
>>>>>           amdgpu_bo_unreserve(robj);
>>>>>           break;
>>>>> +    case AMDGPU_GEM_OP_SET_PRIORITY:
>>>>> +        if (args->value > AMDGPU_BO_PRIORITY_MAX_USER)
>>>>> +            args->value = AMDGPU_BO_PRIORITY_MAX_USER;
>>>>> +        ttm_bo_update_priority(&robj->tbo, args->value);
>>>>> +        if (robj->tbo.evicted_type != TTM_NUM_MEM_TYPES) {
>>>>> +            ttm_bo_try_unevict(&robj->tbo, &ctx);
>>>>> +            amdgpu_bo_unreserve(robj);
>>>>> +        } else {
>>>>> +            amdgpu_bo_unreserve(robj);
>>>>> +            man = ttm_manager_type(robj->tbo.bdev,
>>>>> +                robj->tbo.resource->mem_type);
>>>>> +            ttm_mem_unevict_evicted(robj->tbo.bdev, man,
>>>>> +                        true);
>>>>> +        }
>>>>> +        break;
>>>>>       default:
>>>>>           amdgpu_bo_unreserve(robj);
>>>>>           r = -EINVAL;
>>>>> diff --git a/include/uapi/drm/amdgpu_drm.h
>>>>> b/include/uapi/drm/amdgpu_drm.h
>>>>> index bdbe6b262a78d..53552dd489b9b 100644
>>>>> --- a/include/uapi/drm/amdgpu_drm.h
>>>>> +++ b/include/uapi/drm/amdgpu_drm.h
>>>>> @@ -531,6 +531,7 @@ union drm_amdgpu_wait_fences {
>>>>>
>>>>>   #define AMDGPU_GEM_OP_GET_GEM_CREATE_INFO    0
>>>>>   #define AMDGPU_GEM_OP_SET_PLACEMENT        1
>>>>> +#define AMDGPU_GEM_OP_SET_PRIORITY              2
>>>>>
>>>>>   /* Sets or returns a value associated with a buffer. */
>>>>>   struct drm_amdgpu_gem_op {
>>>>> -- 
>>>>> 2.44.0
>>>>>
>>>>
>>