Re: [PATCH] Enhance perf to collect KVM guest os statistics fromhost side

[Avi Kivity]

On 03/16/2010 09:48 AM, Zhang, Yanmin wrote:
> > Excellent, support for guest kernel != host kernel is critical (I can't
> > remember the last time I ran same kernels).
> >
> > How would we support multiple guests with different kernels?
> >      
> With the patch, 'perf kvm report --sort pid" could show
> summary statistics for all guest os instances. Then, use
> parameter --pid of 'perf kvm record' to collect single problematic instance data.
>    

That certainly works, though automatic association of guest data with 
guest symbols is friendlier.

> > > diff -Nraup linux-2.6_tipmaster0315/arch/x86/kvm/vmx.c linux-2.6_tipmaster0315_perfkvm/arch/x86/kvm/vmx.c
> > > --- linux-2.6_tipmaster0315/arch/x86/kvm/vmx.c	2010-03-16 08:59:11.825295404 +0800
> > > +++ linux-2.6_tipmaster0315_perfkvm/arch/x86/kvm/vmx.c	2010-03-16 09:01:09.976084492 +0800
> > > @@ -26,6 +26,7 @@
> > >    #include<linux/sched.h>
> > >    #include<linux/moduleparam.h>
> > >    #include<linux/ftrace_event.h>
> > > +#include<linux/perf_event.h>
> > >    #include "kvm_cache_regs.h"
> > >    #include "x86.h"
> > >
> > > @@ -3632,6 +3633,43 @@ static void update_cr8_intercept(struct
> > >    	vmcs_write32(TPR_THRESHOLD, irr);
> > >    }
> > >
> > > +DEFINE_PER_CPU(int, kvm_in_guest) = {0};
> > > +
> > > +static void kvm_set_in_guest(void)
> > > +{
> > > +	percpu_write(kvm_in_guest, 1);
> > > +}
> > > +
> > > +static int kvm_is_in_guest(void)
> > > +{
> > > +	return percpu_read(kvm_in_guest);
> > > +}
> > >
> > >        
> >      
>    
> > There is already PF_VCPU for this.
> >      
> Right, but there is a scope between kvm_guest_enter and really running
> in guest os, where a perf event might overflow. Anyway, the scope is very
> narrow, I will change it to use flag PF_VCPU.
>    

There is also a window between setting the flag and calling 'int $2' 
where an NMI might happen and be accounted incorrectly.

Perhaps separate the 'int $2' into a direct call into perf and another 
call for the rest of NMI handling.  I don't see how it would work on svm 
though - AFAICT the NMI is held whereas vmx swallows it.  I guess NMIs 
will be disabled until the next IRET so it isn't racy, just tricky.

> > > +static struct perf_guest_info_callbacks kvm_guest_cbs = {
> > > +	.is_in_guest 		= kvm_is_in_guest,
> > > +	.is_user_mode		= kvm_is_user_mode,
> > > +	.get_guest_ip		= kvm_get_guest_ip,
> > > +	.reset_in_guest		= kvm_reset_in_guest,
> > > +};
> > >
> > >        
> > Should be in common code, not vmx specific.
> >      
> Right. I discussed with Yangsheng. I will move above data structures and
> callbacks to file arch/x86/kvm/x86.c, and add get_ip, a new callback to
> kvm_x86_ops.
>    

You will need access to the vcpu pointer (kvm_rip_read() needs it), you 
can put it in a percpu variable.  I guess if it's not null, you know 
you're in a guest, so no need for PF_VCPU.

--
error compiling committee.c: too many arguments to function

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