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Subject: Re: AMD graphics performance regression in 4.15 and later
To:     =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>,
        Gabriel C <nix.or.die@gmail.com>
Cc:     Dave Airlie <airlied@linux.ie>, alexander.deucher@amd.com,
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        Andrew Morton <akpm@linux-foundation.org>,
        michel.daenzer@amd.com, dri-devel@lists.freedesktop.org,
        LKML <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
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From:   Jean-Marc Valin <jmvalin@mozilla.com>
Message-ID: <7bf2f711-bbd8-cee6-6377-0c4f22db2937@mozilla.com>
Date:   Wed, 11 Apr 2018 14:35:19 -0400
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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