linux-kernel - Re: [REGRESSION] Too-low frequency limit for AMD GPU PCI-passed-through to Windows VM

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Date:   Sat, 29 Jan 2022 19:25:07 -0500
From:   Jim Turner <linuxkernel.foss@...rc-none.turner.link>
To:     "Lazar, Lijo" <lijo.lazar@....com>
Cc:     Alex Deucher <alexdeucher@...il.com>,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        "Deucher, Alexander" <Alexander.Deucher@....com>,
        "regressions@...ts.linux.dev" <regressions@...ts.linux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        "amd-gfx@...ts.freedesktop.org" <amd-gfx@...ts.freedesktop.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Koenig, Christian" <Christian.Koenig@....com>
Subject: Re: [REGRESSION] Too-low frequency limit for AMD GPU
 PCI-passed-through to Windows VM

Hi Lijo,

> Specifically, I was looking for any events happening at these two
> places because of the patch-
>
> https://elixir.bootlin.com/linux/v5.16/source/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c#L411
>
> https://elixir.bootlin.com/linux/v5.16/source/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c#L653

I searched the logs generated with all drm debug messages enabled
(drm.debug=0x1ff) for "device_class", "ATCS", "atcs", "ATIF", and
"atif", for both f1688bd69ec4 and f9b7f3703ff9. Other than the few lines
mentioning ATIF from my previous email, there weren't any matches.

Since "device_class" didn't appear in the logs, we know that
`amdgpu_atif_handler` was not called for either version.

I also patched f9b7f3703ff9 to add the line

  DRM_DEBUG_DRIVER("Entered amdgpu_acpi_pcie_performance_request");

at the top (below the variable declarations) of
`amdgpu_acpi_pcie_performance_request`, and then tested again with all
drm debug messages enabled (0x1ff). That debug message didn't show up.

So, `amdgpu_acpi_pcie_performance_request` was not called either, at
least with f9b7f3703ff9. (I didn't try adding this patch to
f1688bd69ec4.)

Would anything else be helpful?

James