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Date:   Sun, 26 Jul 2020 23:33:48 +1000
From:   Geoffrey McRae <geoff@hostfission.com>
To:     Alex Williamson <alex.williamson@redhat.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 2020-07-26 23:32, Geoffrey McRae wrote:
> On 2020-07-26 23:30, Alex Williamson wrote:
>> 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
> 
> Confirmed:
> 
> https://github.com/torvalds/linux/commit/22540ca3d00d2990a4148a13b92209c3dc5422db

Sorry, I just noticed my error, it should be:
aa202f1f56960c60e7befaa0f49c72b8fa11b0a8

> 
>> 
>>> 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
>>>