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

[Christian König]

Am 15.06.21 um 17:06 schrieb 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.

Ah, yes. That's because we need the pages array for userptr BOs.

Then we should probably move that to amdgpu_ttm_tt_set_userptr().

Thanks,
Christian.

>
> 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;
>>>>>    }
>>>>>