linux-kernel - Re: Kernel and ADM hardware roulette ( was AMD graphics performance regression in 4.15 and later )

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Date:   Thu, 7 Jun 2018 09:07:25 +0200
From:   Christian König <christian.koenig@....com>
To:     Gabriel C <nix.or.die@...il.com>,
        Michel Dänzer <michel@...nzer.net>
Cc:     Jean-Marc Valin <jmvalin@...illa.com>,
        Dave Airlie <airlied@...ux.ie>,
        Felix Kuehling <Felix.Kuehling@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        dri-devel@...ts.freedesktop.org, alexander.deucher@....com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: Kernel and ADM hardware roulette ( was AMD graphics performance
 regression in 4.15 and later )

Am 06.06.2018 um 17:44 schrieb Gabriel C:
> 2018-06-06 17:03 GMT+02:00 Michel Dänzer <michel@...nzer.net>:
>> On 2018-06-06 04:44 PM, Christian König wrote:
>>> Am 06.06.2018 um 16:12 schrieb Michel Dänzer:
>>> [SNIP]
>>> 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@....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@....com>
>>>      Reviewed-by: Monk Liu <monk.liu@....com>
>>>      Reviewed-by: Christian König <christian.koenig@....com>
>>>      Signed-off-by: Alex Deucher <alexander.deucher@....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).

And what I totally missed is that Gabriel is using radeon and not amdgpu.

So Gabriel you need to revert this one for testing:
commit 1bc3d3cce8c3b44c2b5ac6cee98c830bb40e6b0f
Author: Chunming Zhou <david1.zhou@....com>
Date:   Fri Feb 9 10:44:10 2018 +0800

     drm/radeon: only enable swiotlb path when need v2

     swiotlb expands our card accessing range, but its path always is slower
     than ttm pool allocation.
     So add condition to use it.
     v2: move a bit later

     Signed-off-by: Chunming Zhou <david1.zhou@....com>
     Reviewed-by: Monk Liu <monk.liu@....com>
     Reviewed-by: Christian König <christian.koenig@....com>
     Signed-off-by: Alex Deucher <alexander.deucher@....com>
     Link: 
https://patchwork.freedesktop.org/patch/msgid/20180209024410.1469-3-david1.zhou@amd.com

> I got strange performance issue with 4.15 and 4.16 .. but SME was ON
> on that setup ( even before it hit mainline ) and never broke the GPU like this.

Well that is very interesting, you are the first one who reports that 
SME + GFX works in some way. So far we only got negative reports for that.

> There is a 4.16.13 boot dmesg which has no such issue:
>
> http://ftp.frugalware.org/pub/other/people/crazy/radeon/dmesg-radeon-SME-ON-kernel-4.16.txt
>
> With the setup as is booting 4.16.x works , while 4.17 trows the errors.

Please do the bisect if the patch I've mentioned above doesn't help.

Thanks,
Christian.

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