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

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Date:   Wed, 11 Apr 2018 14:35:19 -0400
From:   Jean-Marc Valin <jmvalin@...illa.com>
To:     Christian König <christian.koenig@....com>,
        Gabriel C <nix.or.die@...il.com>
Cc:     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

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.

Cheers,

	Jean-Marc