[PATCH] drm/amdgpu: Adjust the VM size based on system memory size

[Felix Kuehling]

On 2018-08-22 02:55 AM, Christian König wrote:
> Am 21.08.2018 um 23:45 schrieb Felix Kuehling:
[snip]
>> +    } else {
>>> +        struct sysinfo si;
>>> +        unsigned int phys_ram_gb;
>>> +
>>> +        /* Optimal VM size depends on the amount of physical
>>> +         * RAM available. Underlying requirements and
>>> +         * assumptions:
>>> +         *
>>> +         *  - Need to map system memory and VRAM from all GPUs
>>> +         *     - VRAM from other GPUs not known here
>>> +         *     - Assume VRAM <= system memory
>>> +         *  - On GFX8 and older, VM space can be segmented for
>>> +         *    different MTYPEs
>>> +         *  - Need to allow room for fragmentation, guard pages etc.
>>> +         */
>>> +        si_meminfo(&si);
>>> +        phys_ram_gb = ((uint64_t)si.totalram * si.mem_unit) >> 30;
>
> Looks good to me, but I would make sure that round that up before
> shifting it.

Hmm, we used to round up. I just removed it because we were told it's
not necessary.

But I guess rounding up to the next power of two increases the available
VM size without increasing page table size. So we should take it if we
can get it for free. I'll reintroduce rounding up.

>
>>> +        vm_size = min(max(phys_ram_gb * 3, min_vm_size), max_size);
>
> Mhm, "phys_ram_gb * 3"? Maybe add a comment with the rational for that.

Well, the long comment above was meant to justify the factor 3. Maybe I
didn't make that clear enough. 1x is system memory itself, 2x is a wild
guess of VRAM on all GPUs. 3x is room for a second aperture for MTYPE
control, fragmentation and guard pages.

Regards,
  Felix

>
> Christian.
>
>>>       }
>>>         adev->vm_manager.max_pfn = (uint64_t)vm_size << 18;
>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
>>> index 1162c2b..ab1d23e 100644
>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
>>> @@ -345,7 +345,7 @@ struct amdgpu_bo_va_mapping
>>> *amdgpu_vm_bo_lookup_mapping(struct amdgpu_vm *vm,
>>>   void amdgpu_vm_bo_trace_cs(struct amdgpu_vm *vm, struct
>>> ww_acquire_ctx *ticket);
>>>   void amdgpu_vm_bo_rmv(struct amdgpu_device *adev,
>>>                 struct amdgpu_bo_va *bo_va);
>>> -void amdgpu_vm_adjust_size(struct amdgpu_device *adev, uint32_t
>>> vm_size,
>>> +void amdgpu_vm_adjust_size(struct amdgpu_device *adev, uint32_t
>>> min_vm_size,
>>>                  uint32_t fragment_size_default, unsigned max_level,
>>>                  unsigned max_bits);
>>>   int amdgpu_vm_ioctl(struct drm_device *dev, void *data, struct
>>> drm_file *filp);
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>