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

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Date:   Thu, 12 Apr 2018 00:20:24 +0200
From:   Gabriel C <nix.or.die@...il.com>
To:     Jean-Marc Valin <jmvalin@...illa.com>
Cc:     Christian König <christian.koenig@....com>,
        Dave Airlie <airlied@...ux.ie>, alexander.deucher@....com,
        Felix Kuehling <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

2018-04-11 20:35 GMT+02:00 Jean-Marc Valin <jmvalin@...illa.com>:
> On 04/11/2018 05:37 AM, Christian König wrote:
>>> 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.
>
> Well, the hardware appears to be part of the issue too. I don't think
> it's a coincidence that Gabriel has the problem on 2xEPYC, I have it on
> 2xXeon and the previous reported had it on a Core 2 Quad that internally
> has two dies.
>
> I've not yet tested your disable CONFIG_SWIOTLB fix yet -- might try it
> over the weekend and report what happens.
>

To get that right .. is only a matter of disabling SWIOTLB *code*
while CONFIG_SWIOTLB is still set ?