Kernel and ADM hardware roulette ( was AMD graphics performance regression in 4.15 and later )

[Michel Dänzer]

On 2018-06-06 04:44 PM, Christian König wrote:
> Am 06.06.2018 um 16:12 schrieb Michel Dänzer:
>> On 2018-06-06 03:33 PM, Gabriel C wrote:
>>> 2018-06-06 14:19 GMT+02:00 Christian König <christian.koenig at amd.com>:
>>>> Am 06.06.2018 um 14:08 schrieb Gabriel C:
>>>>> 2018-06-06 13:33 GMT+02:00 Christian König <christian.koenig at amd.com>:
>>>>>> Am 06.06.2018 um 13:28 schrieb Gabriel C:
>>
>>>>> http://ftp.frugalware.org/pub/other/people/crazy/radeon/dmesg-iommu-sr-iov-off.txt
>>>>>
>>>>>
>>>>> http://ftp.frugalware.org/pub/other/people/crazy/radeon/dmesg-iommu-sr-iov-on.txt
>>>>>
>>>>>
>>>>> Also nothing else changed in that setup just testing kernel 4.17.
>>>>
>>>>
>>>> That has nothing TODO with the driver nor the original bug you
>>>> reported. The
>>>> problem is that SME is active and that is currently not supported at
>>>> all
>>>> with a that hardware.
>>>
>>> Ok .. so are we playing now kernel an AMD Hardware roulette on each
>>> release ?
>>>
>>> SME was like this in kernel 4.16.x here and all worked.
>>
>> If that is true, again please bisect which commit broke it.
>>
>> All the reports I've seen before this indicated that at least amdgpu
>> has never worked with SME (which BTW doesn't mean it's never going to
>> work or that we don't want to support it, just that as far as we know
>> it's currently not working).
> 
> At least in theory it should work when we use the coherent DMA allocator.
> 
> When that really worked before, so the most likely commit which broke
> this is:
> 
> commit fd5fd480dd8fe4910546e7b080b3ae345e57fe9f
> Author: Chunming Zhou <david1.zhou at amd.com>
> Date:   Fri Feb 9 10:44:09 2018 +0800
> 
>     drm/amdgpu: only enable swiotlb alloc when need v2
> 
>     get the max io mapping address of system memory to see if it is over
>     our card accessing range.
>     v2: move checking later
> 
>     Signed-off-by: Chunming Zhou <david1.zhou at amd.com>
>     Reviewed-by: Monk Liu <monk.liu at amd.com>
>     Reviewed-by: Christian König <christian.koenig at amd.com>
>     Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
> 
> Currently looking into how we could somehow improve this detection.

I guess this could fit for Gabriel, but e.g.
https://bugs.freedesktop.org/104437 says amdgpu was already broken with
SME in 4.15, if not 4.14 (I suspect there was simply no SME support
earlier).


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer