[RFC PATCH] drm/ttm: Do page counting after populate callback succeed

[Felix Kuehling]

Am 2021-06-15 um 8:18 a.m. schrieb Christian König:
> Am 15.06.21 um 14:11 schrieb Pan, Xinhui:
>>> 2021年6月15日 20:01，Christian König <ckoenig.leichtzumerken at gmail.com>
>>> 写道：
>>>
>>> Am 15.06.21 um 13:57 schrieb xinhui pan:
>>>> Amdgpu set SG flag in populate callback. So TTM still count pages
>>>> in SG
>>>> BO.
>>> It's probably better to fix this instead. E.g. why does amdgpu
>>> modify the SG flag during populate and not during initial creation?
>>> That doesn't seem to make sense.
>> fair enough. Let me have a try.
>> No idea why we set SG flag in populate years ago.
>
> That's pretty recent IIRC. Felix moved the code around a bit to fix
> another problem.

I moved some code from populate/unpopulate to backend_bind/unbind for
attaching and detaching dmabufs. I didn't change the setting/unsetting
of SG flags for userptr BOs. That goes back all the way to 2015.

As far as I can tell, this is needed because userptr BOs are not created
as SG BOs. That's something I've also pointed out before.

Regards,
  Felix


>
> Christian.
>
>>
>>> Christian.
>>>
>>>> One easy way to fix this is lets count pages after populate callback.
>>>>
>>>> We hit one issue that amdgpu alloc many SG BOs, but TTM try to do swap
>>>> again and again even if swapout does not swap SG BOs at all.
>>>>
>>>> Signed-off-by: xinhui pan <xinhui.pan at amd.com>
>>>> ---
>>>>   drivers/gpu/drm/ttm/ttm_tt.c | 32 +++++++++++++-------------------
>>>>   1 file changed, 13 insertions(+), 19 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/ttm/ttm_tt.c
>>>> b/drivers/gpu/drm/ttm/ttm_tt.c
>>>> index a1a25410ec74..4fa0a8cd71c0 100644
>>>> --- a/drivers/gpu/drm/ttm/ttm_tt.c
>>>> +++ b/drivers/gpu/drm/ttm/ttm_tt.c
>>>> @@ -317,13 +317,6 @@ int ttm_tt_populate(struct ttm_device *bdev,
>>>>       if (ttm_tt_is_populated(ttm))
>>>>           return 0;
>>>>   -    if (!(ttm->page_flags & TTM_PAGE_FLAG_SG)) {
>>>> -        atomic_long_add(ttm->num_pages, &ttm_pages_allocated);
>>>> -        if (bdev->pool.use_dma32)
>>>> -            atomic_long_add(ttm->num_pages,
>>>> -                    &ttm_dma32_pages_allocated);
>>>> -    }
>>>> -
>>>>       while (atomic_long_read(&ttm_pages_allocated) >
>>>> ttm_pages_limit ||
>>>>              atomic_long_read(&ttm_dma32_pages_allocated) >
>>>>              ttm_dma32_pages_limit) {
>>>> @@ -342,6 +335,13 @@ int ttm_tt_populate(struct ttm_device *bdev,
>>>>       if (ret)
>>>>           goto error;
>>>>   +    if (!(ttm->page_flags & TTM_PAGE_FLAG_SG)) {
>>>> +        atomic_long_add(ttm->num_pages, &ttm_pages_allocated);
>>>> +        if (bdev->pool.use_dma32)
>>>> +            atomic_long_add(ttm->num_pages,
>>>> +                    &ttm_dma32_pages_allocated);
>>>> +    }
>>>> +
>>>>       ttm_tt_add_mapping(bdev, ttm);
>>>>       ttm->page_flags |= TTM_PAGE_FLAG_PRIV_POPULATED;
>>>>       if (unlikely(ttm->page_flags & TTM_PAGE_FLAG_SWAPPED)) {
>>>> @@ -355,12 +355,6 @@ int ttm_tt_populate(struct ttm_device *bdev,
>>>>       return 0;
>>>>     error:
>>>> -    if (!(ttm->page_flags & TTM_PAGE_FLAG_SG)) {
>>>> -        atomic_long_sub(ttm->num_pages, &ttm_pages_allocated);
>>>> -        if (bdev->pool.use_dma32)
>>>> -            atomic_long_sub(ttm->num_pages,
>>>> -                    &ttm_dma32_pages_allocated);
>>>> -    }
>>>>       return ret;
>>>>   }
>>>>   EXPORT_SYMBOL(ttm_tt_populate);
>>>> @@ -384,12 +378,6 @@ void ttm_tt_unpopulate(struct ttm_device
>>>> *bdev, struct ttm_tt *ttm)
>>>>       if (!ttm_tt_is_populated(ttm))
>>>>           return;
>>>>   -    ttm_tt_clear_mapping(ttm);
>>>> -    if (bdev->funcs->ttm_tt_unpopulate)
>>>> -        bdev->funcs->ttm_tt_unpopulate(bdev, ttm);
>>>> -    else
>>>> -        ttm_pool_free(&bdev->pool, ttm);
>>>> -
>>>>       if (!(ttm->page_flags & TTM_PAGE_FLAG_SG)) {
>>>>           atomic_long_sub(ttm->num_pages, &ttm_pages_allocated);
>>>>           if (bdev->pool.use_dma32)
>>>> @@ -397,6 +385,12 @@ void ttm_tt_unpopulate(struct ttm_device
>>>> *bdev, struct ttm_tt *ttm)
>>>>                       &ttm_dma32_pages_allocated);
>>>>       }
>>>>   +    ttm_tt_clear_mapping(ttm);
>>>> +    if (bdev->funcs->ttm_tt_unpopulate)
>>>> +        bdev->funcs->ttm_tt_unpopulate(bdev, ttm);
>>>> +    else
>>>> +        ttm_pool_free(&bdev->pool, ttm);
>>>> +
>>>>       ttm->page_flags &= ~TTM_PAGE_FLAG_PRIV_POPULATED;
>>>>   }
>>>>   
>