Re: [PATCH v1 3/8] KVM: x86: Allocate performance counter for PEBS event

[Peter Zijlstra <peterz@infradead.org>]

On Wed, Oct 30, 2019 at 06:49:42AM +0000, Kang, Luwei wrote:
> > >> >  static void pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type,
> > >> >  				  unsigned config, bool exclude_user,
> > >> >  				  bool exclude_kernel, bool intr,
> > >> > -				  bool in_tx, bool in_tx_cp)
> > >> > +				  bool in_tx, bool in_tx_cp, bool pebs)
> > >> >  {
> > >> >  	struct perf_event *event;
> > >> >  	struct perf_event_attr attr = {
> > >> > @@ -111,9 +111,12 @@ static void pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type,
> > >> >  		.exclude_user = exclude_user,
> > >> >  		.exclude_kernel = exclude_kernel,
> > >> >  		.config = config,
> > >> > +		.precise_ip = pebs ? 1 : 0,
> > >> > +		.aux_output = pebs ? 1 : 0,
> > >>
> > >> srsly?
> > >
> > > Hi Peter,
> > >     Thanks for review. For aux_output, I think it should be set 1 when the guest wants to enabled PEBS by Intel PT.
> > 
> > attr.aux_output==1 means your group leader should be an intel_pt event for this to succeed. Luckily for this instance,
> > perf_event_create_kernel_counter() doesn't actually check the attr.aux_output.
> > 
> > Also, does 'bool pebs' mean PEBS-via-PT or just a PEBS counter? Or does it mean that in kvm it's the same thing?
> 
> It is the same thing. Allocate a counter for PEBS event and use PEBS-via-PT.

It is not the same thing, obviously. It strictly means pebs-over-pt
here.