linux-kernel - Re: AMD graphics performance regression in 4.15 and later

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Date:   Wed, 11 Apr 2018 11:37:45 +0200
From:   Christian König <christian.koenig@....com>
To:     Gabriel C <nix.or.die@...il.com>
Cc:     Jean-Marc Valin <jmvalin@...illa.com>,
        Dave Airlie <airlied@...ux.ie>, alexander.deucher@....com,
        Felix.Kuehling@....com, Laura Abbott <labbott@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        michel.daenzer@....com, dri-devel@...ts.freedesktop.org,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: AMD graphics performance regression in 4.15 and later

Am 11.04.2018 um 06:00 schrieb Gabriel C:
> 2018-04-09 11:42 GMT+02:00 Christian König <ckoenig.leichtzumerken@...il.com>:
>> Am 07.04.2018 um 00:00 schrieb Jean-Marc Valin:
>>> Hi Christian,
>>>
>>> Thanks for the info. FYI, I've also opened a Firefox bug for that at:
>>> https://bugzilla.mozilla.org/show_bug.cgi?id=1448778
>>> Feel free to comment since you have a better understanding of what's
>>> going on.
>>>
>>> One last question: right now I'm running 4.15.0 with the "offending"
>>> patch reverted. Is that safe to run or are there possible bad
>>> interactions with other changes.
>>
>> That should work without problems.
>>
>> But I just had another idea as well, if you want you could still test the
>> new code path which will be using in 4.17.
>>
> While Firefox may do some strange things is not about only Firefox.
>
> With your patches my EPYC box is unusable with  4.15++ kernels.
> The whole Desktop is acting weird.  This one is using
> an Cape Verde PRO [Radeon HD 7750/8740 / R7 250E] GPU.
>
> Box is  2 * EPYC 7281 with 128 GB ECC RAM
>
> Also a 14C Xeon box with a HD7700 is broken same way.

The hardware is irrelevant for this. We need to know what software stack 
you use on top of it.

E.g. desktop environment/Mesa and DDX version etc...

>
> Everything breaks in X .. scrolling , moving windows , flickering etc.
>
>
> reverting f4c809914a7c3e4a59cf543da6c2a15d0f75ee38 and
> 648bc3574716400acc06f99915815f80d9563783
> from an 4.15 kernel makes things work again.
>
>
>> Backporting all the detection logic is to invasive, but you could just go
>> into drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c and forcefull use the other
>> code path.
>>
>> Just look out for "#ifdef CONFIG_SWIOTLB" checks and disable those.
>>
> Well you really can't be serious about these suggestions ? Are you ?
>
> Telling peoples to #if 0 random code is not a solution.

That is for testing and not a permanent solution.

> You broke existsing working userland with your patches and at least
> please fix that for 4.16.
>
> I can help testing code for 4.17/++ if you wish but that is *different* storry.

Please test Alex's amd-staging-drm-next branch from 
git://people.freedesktop.org/~agd5f/linux.

Regards,
Christian.

>
> Regards,
>
> Gabriel C