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

[Christian König]

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.

In other words the priority just tells you which stuff from each app to 
evict first, but not which app to globally throw out.

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
>>>
>>