[vfio-users] Calling ALL VM experts - Seeking assistance with AMD FX CPUs

[Zachary Boley]

Need your vm configs to see if there's anything wrong

On Jan 29, 2017 4:29 AM, "R" <anabstractaffairofone at gmail.com> wrote:

> First time doing this mailing list thing, hopefully I'm doing it right.
>
> Either way, myself and an acquaintance are both using GPU pass-through
> methods to do a bit of gaming on our Linux machines, both running Arch with
> qemu-KVM with a Win10 guest. We've both come across an issue with a
> particular CPU, namely AMD's FX-8320. The best way to describe it would be
> the "rubber banding" experienced in online gaming. We both get mostly
> stable fps, however we both experience this odd effect. The best way it can
> be described would be as if something hangs up, then suddenly lets go,
> causing the game to rush forward to where it should be. It's very much like
> latency in an online match when it suddenly spikes and you see other
> players rush to where they actually are, only offline and in any game.
>
> The current theory has to do with the 8320's FPUs and how they interact
> with CPU pinning, but I think it's more some kind of I/O issue. At least,
> it seems like there's a *bottleneck *somewhere in the system or virtual
> environment causing this any time data is requested. By what? I don't know.
> Said acquaintance is a bit more experienced in this than I am and has tried
> various methods (I don't know the extent) with IRQ nonsenses, where I think
> it may lie to some degree. I simply have the drunken charisma and way with
> words to bring our problem to light.
>
> Either way, it's incredibly annoying. We keep two CPUs for the host, the
> other six are pinned to the VM for whatever it needs though it seems that
> the less cores you apply to the guest, the less the effect is noticed. Most
> everything that can be run on virtio is, and hugepages make no difference.
> What's more, acquaintance is running a 970 chipset and I'm running a 990FX.
> Both our boards properly support this venture. As a clutch, I made sure
> some of the basics with virtio is run with MSI enabled and used, but I've
> only been at this a week. Thus, I'm asking for experts in the field to help
> out.
>
> I've got this far in this, I'd hate to hear it's just the nature of the
> AMD beast and have to chalk it up to time mostly well sepent. If it is
> indeed an FPU issue with the CPU, it makes no sense to me that it'd only
> appear in a virtual environment and not on metal.
>
>
>
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