linux-kernel - Re: [PATCH v2] PCI: Add ATS-disable quirk for AMD Stoney GPUs

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Message-ID: <20170711114948.GA6244@suse.de>
Date:   Tue, 11 Jul 2017 13:49:48 +0200
From:   Joerg Roedel <jroedel@...e.de>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, Daniel Drake <drake@...lessm.com>,
        Alexander Deucher <Alexander.Deucher@....com>,
        Samuel Sieb <samuel@...b.net>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH v2] PCI: Add ATS-disable quirk for AMD Stoney GPUs

Hi Bjorn,

On Mon, Jul 10, 2017 at 11:53:58AM -0500, Bjorn Helgaas wrote:
> I'm still confused.  Per Samuel
> (6dd9dbac-9b65-bc7c-bb08-413a05d09fc8@...b.net):
> 
> Samuel> The other patch seems to fix this issue without disabling ATS.
> Samuel> Isn't that better?
> 
> and Alex
> (BN6PR12MB1652DF4130FC792B71DD9974F7C00@...PR12MB1652.namprd12.prod.outlook.com):
> 
> Alex> I talked to our validation team and ATS was validated on Stoney,
> Alex> so this patch is just working around something else.  The other
> Alex> patch fixes it and is a valid optimization ...
> 
> I'm confused about what this "other patch" is and whether we want that
> one, this one, or both.

The other patches floating around lowered the ATS flush-rate from the
AMD IOMMU driver, which makes the issue disappear as well. But the issue
only disappeared, it is not solved and could probably still be
reproduced with a GPU usage pattern that increases the ATS flush-rate.

So blacklisting the device for ATS is still the safest thing we could do
here.


Regards,

	Joerg