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

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Date:   Wed, 11 Apr 2018 06:00:47 +0200
From:   Gabriel C <nix.or.die@...il.com>
To:     christian.koenig@....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

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.

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.

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.

Regards,

Gabriel C