[PATCH 13/15] drm/amdgpu: adapt vm size for multi vmpt

[Christian König]

Am 28.03.2017 um 05:19 schrieb Zhang, Jerry (Junwei):
> On 03/27/2017 01:53 PM, Chunming Zhou wrote:
>> Change-Id: I17b40aec68404e46961a9fda22dfadd1ae9d6f2c
>> Signed-off-by: Chunming Zhou <David1.Zhou at amd.com>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c 
>> b/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c
>> index 6625a2f..613c8f6 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c
>> @@ -508,6 +508,12 @@ static int gmc_v9_0_vm_init(struct amdgpu_device 
>> *adev)
>>        * amdkfd will use VMIDs 8-15
>>        */
>>       adev->vm_manager.num_ids = AMDGPU_NUM_OF_VMIDS;
>> +    /* Because of four level VMPTs, vm size at least is 256GB.
>> +    256TB is OK as well */
>
> If each PT size is 9, and contains 3 levels PT + 1 PD.
> 9 * 3 + 12(page size) + 1(at least 1 bit for PD) = 40 bits here.
>
> Then it looks 1T is minimum size.
> Please confirm it.

I would rather say completely ignore the setting of amdgpu_vm_size here 
and always use 256TB for GFX9.

Allocating a PD smaller than 4K doesn't make much sense cause you don't 
save anything.

So the only valid approach would be to switch between 1, 2, 3 and 4 
levels when the VM size changes and that doesn't make to much sense to 
me because the saved memory is minimal (4K for each level).

Christian.

>
> Jerry.
>
>> +    if (amdgpu_vm_size < 256) {
>> +        DRM_WARN("vm size at least is 256GB!\n");
>> +        amdgpu_vm_size = 256;
>> +    }
>>       adev->vm_manager.num_level = 1;
>>       amdgpu_vm_manager_init(adev);
>>
>>
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