Messages in this thread | | | Subject | Re: [RFC PATCH] Use vAPIC when doing IPI for PVHVM guests. | From | Juergen Gross <> | Date | Thu, 8 Oct 2015 07:05:49 +0200 |
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On 10/07/2015 10:21 PM, Konrad Rzeszutek Wilk wrote: > Hey, > > I was running some tools in which we would heavily do rescheduling > of events - and realized to my surprise that the event channels (and > the hypercall) would slow things down. If I used the vAPIC with its > IPI support (so no VMEXIT) I got much much better performance. > > Now this is an RFC because: > 1). I hadn't verified from the xentrace how much less VMEXITS we get. > But I remember Boris's patches and they gave at least 10%. > I think this will get the same performance or even better. > > 2). I don't know what to do with migration. That is if the guest > migrates to older hardware it needs to recheck this I presume?
Same problem applies to many other features. In case you want to migrate to a machine with less features you'd have to mask those features in the cpuid data of the domain.
> 3). Should this be enabled by default? I did get better performance > but that was synthetic.
Having some benchmark results would help to decide this. :-)
I'd be especially interested in checking "no vcpu over-commitment" and "heavy vcpu over-commitment" scenarios regarding the effect of the feature.
> > Thoughts?
I like the idea.
Juergen
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