Re: hyper-v support in KVM

[Vadim Rozenfeld <vrozenfe@redhat.com>]

On Wed, 2014-02-12 at 01:33 +0000, Zhang, Yang Z wrote:
> Vadim Rozenfeld wrote on 2014-02-10:
> > On Mon, 2014-02-10 at 08:21 +0000, Zhang, Yang Z wrote:
> >> Hi Vadim,
> >> 
> >> Do you know the latest status of Hyper-v Enlightenments supporting in KVM?
> > Like how many Hyper-v interfaces are supported in KVM?
> > 
> > Hi Yang,
> > 
> > There is no many at the moment. KVM currently supports the following
> > Hyper-V features:
> > 
> > Guest Spinlocks
> > http://msdn.microsoft.com/en-us/library/windows/hardware/ff539081%
> > 28v=vs.85%29.aspx
> > 
> > Local APIC MSR Accesses
> > http://msdn.microsoft.com/en-us/library/windows/hardware/ff542396%
> > 28v=vs.85%29.aspx
> > 
> > Reference Time Counter
> > http://msdn.microsoft.com/en-us/library/windows/hardware/ff542637%
> > 28v=vs.85%29.aspx
> > 
> > We are going to add: Reference TSC Page
> > http://msdn.microsoft.com/en-us/library/windows/hardware/ff542643%
> > 28v=vs.85%29.aspx
> > 
> > Lazy EOI support, maybe more.
> > 
> 
> Thanks for your update. More questions:
> I want to measure the performance improvement with hyper-v features enabled. So I want to know:
> Are those features enabled by default in KVM? 
In KVM - yes, but you also need to specify them in QEMU command line.
They can be enabled by -cpu features hv_vapic, hv_spinlocks, hv_time,
and hv_relaxed

> How to turn off/on it manually? 
Yes. From the QEMU command line.

> And how can I know whether guest is using it really?
There are two options - printk from the KVM side or
WinDbg from the guest side. But in case of hv_time
you can check the value returned by QueryPerformanceFrequency
http://msdn.microsoft.com/en-us/library/windows/desktop/ms644905%
28v=vs.85%29.aspx
it should be 10MHz 

>  Also, Do you have any performance data?
http://www.linux-kvm.org/wiki/images/0/0a/2012-forum-kvm_hyperv.pdf
pp 16, 18
I compared DPC and ISR times with xperf for two cases - with and without
enlightenment.
I also have seen reports mentioned around 5-10 percent CPU usage drop on
the host side, when loading guest with some disk-stress tests. 
  
> 
> > Kind regards.
> > Vadim.
> > 
> >> 
> >> best regards
> >> yang
> >> 
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> > 
> >
> 
> 
> Best regards,
> Yang
> 
>