Re: [Xen-devel] Virtualization of the CPU Performance Monitoring Unit

[Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>]

On Sun, Apr 08, 2012 at 02:48:25PM +0800, Lin Ming wrote:
> On Sat, Apr 7, 2012 at 12:43 AM, Wei Huang <wei.huang2@xxxxxxx> wrote:
> > On 04/06/2012 10:41 AM, Lin Ming wrote:
> >>
> >> Hi list,
> >>
> >> Is anybody working on virtualization of the CPU Performance Monitoring
> >> Unit?
> >>
> >> There are 2 PMU related projects listed on GSoC 2012 page.
> >> http://wiki.xen.org/wiki/Archived/GSoC_2012_Ideas
> >>
> >> - Virtualization of the CPU Performance Monitoring Unit
> >> - Perf support for Xen
> >>
> >> I'm interested on these 2 projects.
> >
> > Hi Lin,
> >
> > 1. I don't think Xen was accepted as an organization for 2012 GSOC. See
> > http://lists.xen.org/archives/html/xen-devel/2012-03/msg02080.html.
> 
> It doesn't matter.
> I just want to find something valuable to do.
> 
> > 2. The PMU project description in the wiki is vague. I know HVM guests
> > support virtualized PMU. Please check vpmu.c files in /hvm, /svm, and /vmx
> > directories. You better ask mentors for details (maybe this is XCP
> > specific?).
> 
> (CC mentors)
> 
> I tested PMU/Perf support with xen-unstable, dom0 3.3 kernel, domU
> 3.4-rc1 kernel.
> Here is the result on an Intel SandyBrige machine.
> 
> - In dom0
> 
> # dmesg |grep -i "Performance Event"
> Performance Events: unsupported p6 CPU model 42 no PMU driver,
> software events only.
> 
> Hardware events are not supported yet in dom0.
> 
> - In domU
> # dmesg |grep -i "Performance Events"
> Performance Events: 16-deep LBR, SandyBridge events, Intel PMU driver.
> 
> Seems domU has support for hardware events.
> But "perf" does not work on domU.

That isn't actually true. If you run it, you will see it working
in the guest - it just that it does not use the performence counters
but instead uses the timer to sample data.

> Run "perf top", but no data was collected.

Hm, I am able to collect data using Fedora Core 16 PV guest.
For dom0 or domU? For dom0 there is a bug somewhere where
the machine crashes after 30 seconds or so - hadn't actually
gotten to the bottom of it. There was an email thread:
https://lkml.org/lkml/2012/2/12/74 about this.

Patches are most welcome!
> 
> # cat /proc/interrupts |grep "PMI"
>  PMI:          0          0   Performance monitoring interrupts
> 
> No PMU interrupts.
> 
> BTW, I also tested KVM-Qemu.
> "perf" works well on KVM-Qemu.
> 
> Thanks,
> Lin Ming
> 
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