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

[Lin Ming <mlin@xxxxxxxxxxxxx>]

On Wed, 2012-04-11 at 09:46 -0400, Konrad Rzeszutek Wilk wrote:
> 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.

Right, I mean "hardware event" does not work.

Hardware event, for example, perf top -e cycles, does not work.
Software event, for example, perf top -e cpu-clock, works.

> 
> > 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

For domU HVM guest.
I have problem to run domU PV guest. Still looking at it.

> 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!

I'll see if I can reproduce this problem on dom0.

Thanks,
Lin Ming


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