[Nouveau] [PATCH 4/6] drm: enable big page mapping for small pages when IOMMU is available

[Vince Hsu]

On 04/17/2015 02:26 PM, Alexandre Courbot wrote:
> On Thu, Apr 16, 2015 at 8:06 PM, Vince Hsu <vinceh at nvidia.com> wrote:
>> Some platforms have IOMMU to map non-contiguous physical memory into
>> contiguous GPU virtual address. We can use this feature to enable big pages
>> mapping on scattered small pages. To achieve that, we also need changes in
>> subdev/mmu as well.
>>
>> Signed-off-by: Vince Hsu <vinceh at nvidia.com>
>> ---
>>   drm/nouveau/nouveau_bo.c | 9 +++++++++
>>   1 file changed, 9 insertions(+)
>>
>> diff --git a/drm/nouveau/nouveau_bo.c b/drm/nouveau/nouveau_bo.c
>> index 77326e344dad..da76ee1121e4 100644
>> --- a/drm/nouveau/nouveau_bo.c
>> +++ b/drm/nouveau/nouveau_bo.c
>> @@ -221,6 +221,11 @@ nouveau_bo_new(struct drm_device *dev, int size, int align,
>>          if (drm->client.vm) {
>>                  if (!(flags & TTM_PL_FLAG_TT) && size > 256 * 1024)
>>                          nvbo->page_shift = drm->client.vm->mmu->lpg_shift;
>> +
>> +               if ((flags & TTM_PL_FLAG_TT) &&
>> +                               drm->client.vm->mmu->iommu_capable &&
>> +                               (size % (1 << drm->client.vm->mmu->lpg_shift)) == 0)
>> +                       nvbo->page_shift = drm->client.vm->mmu->lpg_shift;
> I wonder if we should not just use the same size heuristics as for VRAM above?
>
> Here, unless your buffer size is an exact multiple of the big page
> size (128K for GK20A), you will not use big pages at all. In effect,
> many buffers will be rejected for this reason. A behavior like "if the
> buffer size of more than 256KB, increase the size of the buffer to the
> next multiple of 128K and use big pages" would probably yield better
> results.
I'm told that the user space would align the buffer to the big page 
size. So I made this patch based on that impression. I'm not pretty 
familiar with the user space behavior, so sorry if I say something wrong 
here.

And are we allowed to extend the buffer size even the exporter doesn't 
know about that?

>>          }
>>
>>          nouveau_bo_fixup_align(nvbo, flags, &align, &size);
>> @@ -1641,6 +1646,10 @@ nouveau_bo_vma_add(struct nouveau_bo *nvbo, struct nvkm_vm *vm,
>>              (nvbo->bo.mem.mem_type == TTM_PL_VRAM ||
>>               nvbo->page_shift != vma->vm->mmu->lpg_shift))
>>                  nvkm_vm_map(vma, nvbo->bo.mem.mm_node);
>> +       else if (nvbo->bo.mem.mem_type == TTM_PL_TT &&
>> +               vma->vm->mmu->iommu_capable &&
>> +               nvbo->page_shift == vma->vm->mmu->lpg_shift)
>> +               nvkm_vm_map(vma, nvbo->bo.mem.mm_node);
> Sorry, I don't understand why this is needed, could you explain?
Originally the buffer can only be mapped when the memory type is VRAM or 
the page is small. So I added another condition to map big page for TT.

Thanks,
Vince





-----------------------------------------------------------------------------------
This email message is for the sole use of the intended recipient(s) and may contain
confidential information.  Any unauthorized review, use, disclosure or distribution
is prohibited.  If you are not the intended recipient, please contact the sender by
reply email and destroy all copies of the original message.
-----------------------------------------------------------------------------------