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Date:   Sun, 26 Jul 2020 07:30:52 -0600
From:   Alex Williamson <alex.williamson@redhat.com>
To:     Geoffrey McRae <geoff@hostfission.com>
Cc:     hdanton@sina.com, tj@kernel.org, jiangshanlai@gmail.com,
        linux-kernel@vger.kernel.org
Subject: Re: Poor windows VFIO performance, GPU stalls (bisected)
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On Sun, 26 Jul 2020 17:49:07 +1000
Geoffrey McRae <geoff@hostfission.com> wrote:

> Hi All,
> 
> The commit 22540ca3d00d2990a4148a13b92209c3dc5422db causes a Windows KVM 
> guest running under QEMU with a VFIO passthrough GPU to randomly stall 
> when using the GPU leading to the guest assuming that the driver has 
> hung. Reverting this commit resolves the problem.

Please double check this commit ID, I can't find it in mainline or
linux-next.  Thanks,

Alex
 
> The host system is configured with the following kernel arguments which 
> may be related:
>    isolcpus=0-5,24-29,6-11,30-35 rcu_nocbs=0-5,24-29,6-11,30-35
> 
> The system is an AMD Threadripper 2970WX on a Gigabyte x399 AORUS Gaming 
> 7 board.
> It has two GPUs each being passed through to two separate KVM guests, 
> one is an AMD Radeon 7 in a Linux guest, the other is a GeForce 1080Ti 
> in a Windows guest.
> The cores used for these two guests are isolated from the host for 
> performance reasons.
> 
> Any insight as to why this is occurring would be appreciated. If you 
> need any more information or would like to test patches please let me 
> know.
> 
> Kind Regards,
> Geoffrey McRae
> HostFission
> 
> https://hostfission.com
>