[vfio-users] Eliminate Mini Stutter in "Witcher 3: The Wild Hunt" on top of KVM/VFIO

[Alex Williamson]

On Tue, Mar 15, 2016 at 10:25 PM, Okky Hendriansyah <okky.htf at gmail.com>
wrote:

> Hi All,
>
> I experienced a very noticeable mini stutters here and there when playing
> "Witcher 3: The Wild Hunt" on my Windows 10 VM with OVMF and MSI enabled. I
> was using the official linux-lts-4.1.19-1 from Arch Linux repository.
> Apparently after changing these 3 kernel configurations and recompile the
> kernel, the mini stutter issues are gone!
>
> Here are the kernel configuration that I changed:
> 1.) 1000 MHz clock resolution
> 2.) Voluntary preemption scheduling
> 3.) Madvise hugepages (not really sure that this changes anything actually)
>
> I am not really sure whether all or just one of them specifically
> eliminate the mini stuttering. If someone had any idea what is really going
> on, my ears are open. I found the kernel config changes from nbhs' early
> post [1] and since my VM disk is on ZFS  [2].
>

The Fedora kernel already sets all of these, however regarding 3) the
advice from nbhs is to use hugetlbfs and not rely on transparent
hugepages.  Transparent hugepages is not compatible with device assignment
since pages get pinned as the VM is created, there's no opportunity for
transparent hugepages to take effect.  Therefore I don't think your madvise
change is doing anything.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://listman.redhat.com/archives/vfio-users/attachments/20160315/1d392360/attachment.htm>