Re: Poor windows VFIO performance, GPU stalls (bisected)

[Geoffrey McRae <geoff@hostfission.com>]

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

> 
>> 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
>>