Re: High vm-exit latencies during kvm boot-up/shutdown

[Dor Laor <dor.laor-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Dong, Eddie wrote:
>
> Jan Kiszka wrote:
> >
> > So if you want the higher performance of PCIe you need
> > performance-killing wbindv (not to speak of latency)? That sounds a
> > bit contradictory to me. So this is also true for native PCIe usage?
> >
>
> Mmm, I won't say so. When you want to get RT performance, you
> won't use unknown OS such as Windows. If you use your RT
> linux, the OS (guest) itself should not use wbinvd.
>
The idea is to have a RT-Linux on the host that runs RT jobs but also
use it to run mgmt/other code on windows guests.
This way you can better utilize an idle RT linux while keeping
short latencies for the RT jobs.
Dor.
>
> For the Bochs BIOS case, like Avi mentioned, we can simply remove it.
>
>
> > What really frightens me about wbinvd is that its latency "nicely"
> > scales with the cache sizes. And I think my observed latency
> > is far from
> > being the worst case. In a different experiment, I once measured
> > wbinvd latencies of a few milliseconds... :(
> >
> I don't know details, but it could be. While RT usage can easily remove
> this instruction.
>
> thx,eddie
>
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