Re: [PATCH 1/9] drm/amdgpu: generally allow over-commit during BO allocation

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

Am 10.12.22 um 07:15 schrieb Felix Kuehling:
> On 2022-11-25 05:21, Christian König wrote:
>> We already fallback to a dummy BO with no backing store when we
>> allocate GDS,GWS and OA resources and to GTT when we allocate VRAM.
>>
>> Drop all those workarounds and generalize this for GTT as well. This
>> fixes ENOMEM issues with runaway applications which try to allocate/free
>> GTT in a loop and are otherwise only limited by the CPU speed.
>>
>> The CS will wait for the cleanup of freed up BOs to satisfy the
>> various domain specific limits and so effectively throttle those
>> buggy applications down to a sane allocation behavior again.
>>
>> Signed-off-by: Christian König <christian.koenig@amd.com>
>
> This patch causes some regressions in KFDTest. KFDMemoryTest.MMBench 
> sees a huge VRAM allocation slow-down. And 
> KFDMemoryTest.LargestVramBufferTest can only allocate half the 
> available memory.

Mhm, I wasn't expecting that we use this for the KFD as well.

>
> This seems to be caused by initially validating VRAM BOs in the CPU 
> domain, which allocates a ttm_tt. A subsequent validation in the VRAM 
> domain involves a copy from GTT to VRAM.

The idea was to initially create the BOs without any backing store.

>
> After that, freeing of BOs can get delayed by the ghost object of a 
> previous migration, which delays calling release notifiers and causes 
> problems for KFDs available memory accounting.
>
> I experimented with a workaround that validates BOs immediately after 
> allocation, but that only moves around the delays and doesn't solve 
> the problem. During those experiments I may also have stumbled over a 
> bug in ttm_buffer_object_transfer: It calls ttm_bo_set_bulk_move 
> before initializing and locking fbo->base.base._resv. This results in 
> a flood of warnings because ttm_bo_set_bulk_move expects the 
> reservation to be locked.
>
> Right now I'd like to remove the bp.domain = initial_domain | 
> AMDGPU_GEM_DOMAIN_CPU change in amdgpu_gem_object_create to fix this.

Yeah, let's revert and investigate this first.

Thanks,
Christian.

>
> Regards,
>   Felix
>
>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c    | 16 +++-------------
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_object.c |  6 +-----
>>   2 files changed, 4 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c 
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>> index a0780a4e3e61..62e98f1ad770 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>> @@ -113,7 +113,7 @@ int amdgpu_gem_object_create(struct amdgpu_device 
>> *adev, unsigned long size,
>>       bp.resv = resv;
>>       bp.preferred_domain = initial_domain;
>>       bp.flags = flags;
>> -    bp.domain = initial_domain;
>> +    bp.domain = initial_domain | AMDGPU_GEM_DOMAIN_CPU;
>>       bp.bo_ptr_size = sizeof(struct amdgpu_bo);
>>         r = amdgpu_bo_create_user(adev, &bp, &ubo);
>> @@ -332,20 +332,10 @@ int amdgpu_gem_create_ioctl(struct drm_device 
>> *dev, void *data,
>>       }
>>         initial_domain = (u32)(0xffffffff & args->in.domains);
>> -retry:
>>       r = amdgpu_gem_object_create(adev, size, args->in.alignment,
>> -                     initial_domain,
>> -                     flags, ttm_bo_type_device, resv, &gobj);
>> +                     initial_domain, flags, ttm_bo_type_device,
>> +                     resv, &gobj);
>>       if (r && r != -ERESTARTSYS) {
>> -        if (flags & AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED) {
>> -            flags &= ~AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED;
>> -            goto retry;
>> -        }
>> -
>> -        if (initial_domain == AMDGPU_GEM_DOMAIN_VRAM) {
>> -            initial_domain |= AMDGPU_GEM_DOMAIN_GTT;
>> -            goto retry;
>> -        }
>>           DRM_DEBUG("Failed to allocate GEM object (%llu, %d, %llu, 
>> %d)\n",
>>                   size, initial_domain, args->in.alignment, r);
>>       }
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c 
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
>> index 974e85d8b6cc..919bbea2e3ac 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
>> @@ -581,11 +581,7 @@ int amdgpu_bo_create(struct amdgpu_device *adev,
>>           bo->flags |= AMDGPU_GEM_CREATE_VRAM_WIPE_ON_RELEASE;
>>         bo->tbo.bdev = &adev->mman.bdev;
>> -    if (bp->domain & (AMDGPU_GEM_DOMAIN_GWS | AMDGPU_GEM_DOMAIN_OA |
>> -              AMDGPU_GEM_DOMAIN_GDS))
>> -        amdgpu_bo_placement_from_domain(bo, AMDGPU_GEM_DOMAIN_CPU);
>> -    else
>> -        amdgpu_bo_placement_from_domain(bo, bp->domain);
>> +    amdgpu_bo_placement_from_domain(bo, bp->domain);
>>       if (bp->type == ttm_bo_type_kernel)
>>           bo->tbo.priority = 1;