[PATCH 1/1] perf/x86: filter branches for PEBS event

[PATCH 1/1] perf/x86: filter branches for PEBS event

[kan.liang]

From: Kan Liang <kan.liang@intel.com>

For supporting Intel LBR branches filtering, Intel LBR sharing logic
mechanism is introduced from commit b36817e88630 ("perf/x86: Add Intel
LBR sharing logic"). It modifies __intel_shared_reg_get_constraints to
config lbr_sel, which is finally used to set LBR_SELECT.
However, the intel_shared_regs_constraints is called after
intel_pebs_constraints. The PEBS event will return immediately after
intel_pebs_constraints. So it's impossible to filter branches for PEBS
event.

This patch move intel_shared_regs_constraints for branch_reg ahead of
intel_pebs_constraints.
intel_shared_regs_constraints for branch_reg doesn't modify event->hw,
so it's safe to be called before intel_pebs_constraints.
intel_shared_regs_constraints for branch_reg also special case when it
returns &emptyconstraint. It put constraints for extra_reg. This patch
remove it. Because it will never get constraints for extra_reg if return
is &emptyconstraint.

Signed-off-by: Kan Liang <kan.liang@intel.com>
---
 arch/x86/kernel/cpu/perf_event_intel.c | 34 ++++++++++++----------------------
 1 file changed, 12 insertions(+), 22 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index 9f1dd18..247780a 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -1587,25 +1587,14 @@ __intel_shared_reg_put_constraints(struct cpu_hw_events *cpuc,
 
 static struct event_constraint *
 intel_shared_regs_constraints(struct cpu_hw_events *cpuc,
-			      struct perf_event *event)
+			      struct perf_event *event,
+			      struct hw_perf_event_extra *reg)
 {
-	struct event_constraint *c = NULL, *d;
-	struct hw_perf_event_extra *xreg, *breg;
+	struct event_constraint *c = NULL;
+
+	if (reg->idx != EXTRA_REG_NONE)
+		c = __intel_shared_reg_get_constraints(cpuc, event, reg);
 
-	xreg = &event->hw.extra_reg;
-	if (xreg->idx != EXTRA_REG_NONE) {
-		c = __intel_shared_reg_get_constraints(cpuc, event, xreg);
-		if (c == &emptyconstraint)
-			return c;
-	}
-	breg = &event->hw.branch_reg;
-	if (breg->idx != EXTRA_REG_NONE) {
-		d = __intel_shared_reg_get_constraints(cpuc, event, breg);
-		if (d == &emptyconstraint) {
-			__intel_shared_reg_put_constraints(cpuc, xreg);
-			c = d;
-		}
-	}
 	return c;
 }
 
@@ -1629,17 +1618,18 @@ x86_get_event_constraints(struct cpu_hw_events *cpuc, struct perf_event *event)
 static struct event_constraint *
 intel_get_event_constraints(struct cpu_hw_events *cpuc, struct perf_event *event)
 {
-	struct event_constraint *c;
+	struct event_constraint *c, *d;
 
 	c = intel_bts_constraints(event);
 	if (c)
 		return c;
 
-	c = intel_pebs_constraints(event);
-	if (c)
-		return c;
+	c = intel_shared_regs_constraints(cpuc, event, &event->hw.branch_reg);
+	d = intel_pebs_constraints(event);
+	if (d || c)
+		return (d) ? (d) : (c);
 
-	c = intel_shared_regs_constraints(cpuc, event);
+	c = intel_shared_regs_constraints(cpuc, event, &event->hw.extra_reg);
 	if (c)
 		return c;
 
-- 
1.8.3.2

Re: [PATCH 1/1] perf/x86: filter branches for PEBS event

[Stephane Eranian]

On Thu, Mar 26, 2015 at 11:13 AM,  <kan.liang@intel.com> wrote:
> From: Kan Liang <kan.liang@intel.com>
>
> For supporting Intel LBR branches filtering, Intel LBR sharing logic
> mechanism is introduced from commit b36817e88630 ("perf/x86: Add Intel
> LBR sharing logic"). It modifies __intel_shared_reg_get_constraints to
> config lbr_sel, which is finally used to set LBR_SELECT.
> However, the intel_shared_regs_constraints is called after
> intel_pebs_constraints. The PEBS event will return immediately after
> intel_pebs_constraints. So it's impossible to filter branches for PEBS
> event.
>
> This patch move intel_shared_regs_constraints for branch_reg ahead of
> intel_pebs_constraints.
> intel_shared_regs_constraints for branch_reg doesn't modify event->hw,
> so it's safe to be called before intel_pebs_constraints.
> intel_shared_regs_constraints for branch_reg also special case when it
> returns &emptyconstraint. It put constraints for extra_reg. This patch
> remove it. Because it will never get constraints for extra_reg if return
> is &emptyconstraint.
>
> Signed-off-by: Kan Liang <kan.liang@intel.com>
> ---
>  arch/x86/kernel/cpu/perf_event_intel.c | 34 ++++++++++++----------------------
>  1 file changed, 12 insertions(+), 22 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
> index 9f1dd18..247780a 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel.c
> @@ -1587,25 +1587,14 @@ __intel_shared_reg_put_constraints(struct cpu_hw_events *cpuc,
>
>  static struct event_constraint *
>  intel_shared_regs_constraints(struct cpu_hw_events *cpuc,
> -                             struct perf_event *event)
> +                             struct perf_event *event,
> +                             struct hw_perf_event_extra *reg)
>  {
> -       struct event_constraint *c = NULL, *d;
> -       struct hw_perf_event_extra *xreg, *breg;
> +       struct event_constraint *c = NULL;
> +
> +       if (reg->idx != EXTRA_REG_NONE)
> +               c = __intel_shared_reg_get_constraints(cpuc, event, reg);
>
> -       xreg = &event->hw.extra_reg;
> -       if (xreg->idx != EXTRA_REG_NONE) {
> -               c = __intel_shared_reg_get_constraints(cpuc, event, xreg);
> -               if (c == &emptyconstraint)
> -                       return c;
> -       }
> -       breg = &event->hw.branch_reg;
> -       if (breg->idx != EXTRA_REG_NONE) {
> -               d = __intel_shared_reg_get_constraints(cpuc, event, breg);
> -               if (d == &emptyconstraint) {
> -                       __intel_shared_reg_put_constraints(cpuc, xreg);
> -                       c = d;
> -               }
> -       }
>         return c;
>  }
>
> @@ -1629,17 +1618,18 @@ x86_get_event_constraints(struct cpu_hw_events *cpuc, struct perf_event *event)
>  static struct event_constraint *
>  intel_get_event_constraints(struct cpu_hw_events *cpuc, struct perf_event *event)
>  {
> -       struct event_constraint *c;
> +       struct event_constraint *c, *d;
>
>         c = intel_bts_constraints(event);
>         if (c)
>                 return c;
>
> -       c = intel_pebs_constraints(event);
> -       if (c)
> -               return c;
> +       c = intel_shared_regs_constraints(cpuc, event, &event->hw.branch_reg);
> +       d = intel_pebs_constraints(event);
> +       if (d || c)
> +               return (d) ? (d) : (c);
>
> -       c = intel_shared_regs_constraints(cpuc, event);
> +       c = intel_shared_regs_constraints(cpuc, event, &event->hw.extra_reg);
>         if (c)
>                 return c;
>
You are addressing one of the problems of this routine. But I think
there is a more serious
issue which is not addressed here. The intel_shared_regs_constraints()
assumes that
the associated event is necessarily unconstrained:

__intel_shared_reg_get_constraints()
{
    struct event_constraint *c = &emptyconstraint;
   ...
}

This is true for offcore_response, but for LBR this may not always be the case.
I may want to use LBR on the L1D_PEND_MISS event and it would need to
be on counter 2. But I believe that the current code could place it on counter 0
simply because you return if shared_reg_get_constraint() is successful, but
it looks only at the LBR constraint not the event constraint. I think
in the presence
of LBR, you always need to call share_get_reg() and x86_get_event_constraint().
This is to ensure that both the shared constraint AND the event constraint are
satisfied (and of course, in case one fails, the other needs to be released).


> --
> 1.8.3.2
>

RE: [PATCH 1/1] perf/x86: filter branches for PEBS event

[Liang, Kan]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="utf-8", Size: 5602 bytes --]



> Subject: Re: [PATCH 1/1] perf/x86: filter branches for PEBS event
> 
> On Thu, Mar 26, 2015 at 11:13 AM,  <kan.liang@intel.com> wrote:
> > From: Kan Liang <kan.liang@intel.com>
> >
> > For supporting Intel LBR branches filtering, Intel LBR sharing logic
> > mechanism is introduced from commit b36817e88630 ("perf/x86: Add
> Intel
> > LBR sharing logic"). It modifies __intel_shared_reg_get_constraints to
> > config lbr_sel, which is finally used to set LBR_SELECT.
> > However, the intel_shared_regs_constraints is called after
> > intel_pebs_constraints. The PEBS event will return immediately after
> > intel_pebs_constraints. So it's impossible to filter branches for PEBS
> > event.
> >
> > This patch move intel_shared_regs_constraints for branch_reg ahead of
> > intel_pebs_constraints.
> > intel_shared_regs_constraints for branch_reg doesn't modify event->hw,
> > so it's safe to be called before intel_pebs_constraints.
> > intel_shared_regs_constraints for branch_reg also special case when it
> > returns &emptyconstraint. It put constraints for extra_reg. This patch
> > remove it. Because it will never get constraints for extra_reg if
> > return is &emptyconstraint.
> >
> > Signed-off-by: Kan Liang <kan.liang@intel.com>
> > ---
> >  arch/x86/kernel/cpu/perf_event_intel.c | 34
> > ++++++++++++----------------------
> >  1 file changed, 12 insertions(+), 22 deletions(-)
> >
> > diff --git a/arch/x86/kernel/cpu/perf_event_intel.c
> > b/arch/x86/kernel/cpu/perf_event_intel.c
> > index 9f1dd18..247780a 100644
> > --- a/arch/x86/kernel/cpu/perf_event_intel.c
> > +++ b/arch/x86/kernel/cpu/perf_event_intel.c
> > @@ -1587,25 +1587,14 @@ __intel_shared_reg_put_constraints(struct
> > cpu_hw_events *cpuc,
> >
> >  static struct event_constraint *
> >  intel_shared_regs_constraints(struct cpu_hw_events *cpuc,
> > -                             struct perf_event *event)
> > +                             struct perf_event *event,
> > +                             struct hw_perf_event_extra *reg)
> >  {
> > -       struct event_constraint *c = NULL, *d;
> > -       struct hw_perf_event_extra *xreg, *breg;
> > +       struct event_constraint *c = NULL;
> > +
> > +       if (reg->idx != EXTRA_REG_NONE)
> > +               c = __intel_shared_reg_get_constraints(cpuc, event,
> > + reg);
> >
> > -       xreg = &event->hw.extra_reg;
> > -       if (xreg->idx != EXTRA_REG_NONE) {
> > -               c = __intel_shared_reg_get_constraints(cpuc, event, xreg);
> > -               if (c == &emptyconstraint)
> > -                       return c;
> > -       }
> > -       breg = &event->hw.branch_reg;
> > -       if (breg->idx != EXTRA_REG_NONE) {
> > -               d = __intel_shared_reg_get_constraints(cpuc, event, breg);
> > -               if (d == &emptyconstraint) {
> > -                       __intel_shared_reg_put_constraints(cpuc, xreg);
> > -                       c = d;
> > -               }
> > -       }
> >         return c;
> >  }
> >
> > @@ -1629,17 +1618,18 @@ x86_get_event_constraints(struct
> cpu_hw_events
> > *cpuc, struct perf_event *event)  static struct event_constraint *
> > intel_get_event_constraints(struct cpu_hw_events *cpuc, struct
> > perf_event *event)  {
> > -       struct event_constraint *c;
> > +       struct event_constraint *c, *d;
> >
> >         c = intel_bts_constraints(event);
> >         if (c)
> >                 return c;
> >
> > -       c = intel_pebs_constraints(event);
> > -       if (c)
> > -               return c;
> > +       c = intel_shared_regs_constraints(cpuc, event, &event-
> >hw.branch_reg);
> > +       d = intel_pebs_constraints(event);
> > +       if (d || c)
> > +               return (d) ? (d) : (c);
> >
> > -       c = intel_shared_regs_constraints(cpuc, event);
> > +       c = intel_shared_regs_constraints(cpuc, event,
> > + &event->hw.extra_reg);
> >         if (c)
> >                 return c;
> >
> You are addressing one of the problems of this routine. But I think there is
> a more serious issue which is not addressed here. The
> intel_shared_regs_constraints() assumes that the associated event is
> necessarily unconstrained:
> 
> __intel_shared_reg_get_constraints()
> {
>     struct event_constraint *c = &emptyconstraint;
>    ...
> }
> 
> This is true for offcore_response, but for LBR this may not always be the
> case.
> I may want to use LBR on the L1D_PEND_MISS event and it would need to
> be on counter 2. But I believe that the current code could place it on
> counter 0 simply because you return if shared_reg_get_constraint() is
> successful, but it looks only at the LBR constraint not the event constraint. 

I didn’t change __intel_shared_reg_get_constraints and its input. 
So using LBR on the L1D_PEND_MISS event, it would return NULL.
		/*
		 * need to call x86_get_event_constraint()
		 * to check if associated event has constraints
		 */
		c = NULL;
Since it's not PEBS, intel_pebs_constraints will also return NULL.
So it will not return. It will continue to check extra_reg and finally
check if associated event has constraints.
>I
> think in the presence of LBR, you always need to call share_get_reg() and
> x86_get_event_constraint().
> This is to ensure that both the shared constraint AND the event constraint
> are satisfied (and of course, in case one fails, the other needs to be
> released).
> 
The patch doesn't change the behavior for non-PEBS event.

Thanks,
Kan
> 
> > --
> > 1.8.3.2
> >
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Re: [PATCH 1/1] perf/x86: filter branches for PEBS event

[Stephane Eranian]

On Thu, Mar 26, 2015 at 1:20 PM, Liang, Kan <kan.liang@intel.com> wrote:
>
>
>> Subject: Re: [PATCH 1/1] perf/x86: filter branches for PEBS event
>>
>> On Thu, Mar 26, 2015 at 11:13 AM,  <kan.liang@intel.com> wrote:
>> > From: Kan Liang <kan.liang@intel.com>
>> >
>> > For supporting Intel LBR branches filtering, Intel LBR sharing logic
>> > mechanism is introduced from commit b36817e88630 ("perf/x86: Add
>> Intel
>> > LBR sharing logic"). It modifies __intel_shared_reg_get_constraints to
>> > config lbr_sel, which is finally used to set LBR_SELECT.
>> > However, the intel_shared_regs_constraints is called after
>> > intel_pebs_constraints. The PEBS event will return immediately after
>> > intel_pebs_constraints. So it's impossible to filter branches for PEBS
>> > event.
>> >
>> > This patch move intel_shared_regs_constraints for branch_reg ahead of
>> > intel_pebs_constraints.
>> > intel_shared_regs_constraints for branch_reg doesn't modify event->hw,
>> > so it's safe to be called before intel_pebs_constraints.
>> > intel_shared_regs_constraints for branch_reg also special case when it
>> > returns &emptyconstraint. It put constraints for extra_reg. This patch
>> > remove it. Because it will never get constraints for extra_reg if
>> > return is &emptyconstraint.
>> >
>> > Signed-off-by: Kan Liang <kan.liang@intel.com>
>> > ---
>> >  arch/x86/kernel/cpu/perf_event_intel.c | 34
>> > ++++++++++++----------------------
>> >  1 file changed, 12 insertions(+), 22 deletions(-)
>> >
>> > diff --git a/arch/x86/kernel/cpu/perf_event_intel.c
>> > b/arch/x86/kernel/cpu/perf_event_intel.c
>> > index 9f1dd18..247780a 100644
>> > --- a/arch/x86/kernel/cpu/perf_event_intel.c
>> > +++ b/arch/x86/kernel/cpu/perf_event_intel.c
>> > @@ -1587,25 +1587,14 @@ __intel_shared_reg_put_constraints(struct
>> > cpu_hw_events *cpuc,
>> >
>> >  static struct event_constraint *
>> >  intel_shared_regs_constraints(struct cpu_hw_events *cpuc,
>> > -                             struct perf_event *event)
>> > +                             struct perf_event *event,
>> > +                             struct hw_perf_event_extra *reg)
>> >  {
>> > -       struct event_constraint *c = NULL, *d;
>> > -       struct hw_perf_event_extra *xreg, *breg;
>> > +       struct event_constraint *c = NULL;
>> > +
>> > +       if (reg->idx != EXTRA_REG_NONE)
>> > +               c = __intel_shared_reg_get_constraints(cpuc, event,
>> > + reg);
>> >
>> > -       xreg = &event->hw.extra_reg;
>> > -       if (xreg->idx != EXTRA_REG_NONE) {
>> > -               c = __intel_shared_reg_get_constraints(cpuc, event, xreg);
>> > -               if (c == &emptyconstraint)
>> > -                       return c;
>> > -       }
>> > -       breg = &event->hw.branch_reg;
>> > -       if (breg->idx != EXTRA_REG_NONE) {
>> > -               d = __intel_shared_reg_get_constraints(cpuc, event, breg);
>> > -               if (d == &emptyconstraint) {
>> > -                       __intel_shared_reg_put_constraints(cpuc, xreg);
>> > -                       c = d;
>> > -               }
>> > -       }
>> >         return c;
>> >  }
>> >
>> > @@ -1629,17 +1618,18 @@ x86_get_event_constraints(struct
>> cpu_hw_events
>> > *cpuc, struct perf_event *event)  static struct event_constraint *
>> > intel_get_event_constraints(struct cpu_hw_events *cpuc, struct
>> > perf_event *event)  {
>> > -       struct event_constraint *c;
>> > +       struct event_constraint *c, *d;
>> >
>> >         c = intel_bts_constraints(event);
>> >         if (c)
>> >                 return c;
>> >
>> > -       c = intel_pebs_constraints(event);
>> > -       if (c)
>> > -               return c;
>> > +       c = intel_shared_regs_constraints(cpuc, event, &event-
>> >hw.branch_reg);
>> > +       d = intel_pebs_constraints(event);
>> > +       if (d || c)
>> > +               return (d) ? (d) : (c);
>> >
>> > -       c = intel_shared_regs_constraints(cpuc, event);
>> > +       c = intel_shared_regs_constraints(cpuc, event,
>> > + &event->hw.extra_reg);
>> >         if (c)
>> >                 return c;
>> >
>> You are addressing one of the problems of this routine. But I think there is
>> a more serious issue which is not addressed here. The
>> intel_shared_regs_constraints() assumes that the associated event is
>> necessarily unconstrained:
>>
>> __intel_shared_reg_get_constraints()
>> {
>>     struct event_constraint *c = &emptyconstraint;
>>    ...
>> }
>>
>> This is true for offcore_response, but for LBR this may not always be the
>> case.
>> I may want to use LBR on the L1D_PEND_MISS event and it would need to
>> be on counter 2. But I believe that the current code could place it on
>> counter 0 simply because you return if shared_reg_get_constraint() is
>> successful, but it looks only at the LBR constraint not the event constraint.
>
> I didn’t change __intel_shared_reg_get_constraints and its input.
> So using LBR on the L1D_PEND_MISS event, it would return NULL.
>                 /*
>                  * need to call x86_get_event_constraint()
>                  * to check if associated event has constraints
>                  */
>                 c = NULL;
> Since it's not PEBS, intel_pebs_constraints will also return NULL.
> So it will not return. It will continue to check extra_reg and finally
> check if associated event has constraints.
>>I
>> think in the presence of LBR, you always need to call share_get_reg() and
>> x86_get_event_constraint().
>> This is to ensure that both the shared constraint AND the event constraint
>> are satisfied (and of course, in case one fails, the other needs to be
>> released).
>>
> The patch doesn't change the behavior for non-PEBS event.
>
I know that. I was commenting in general on the function. I think it still has
the problem I mention. And it needs to be fixed.

> Thanks,
> Kan
>>
>> > --
>> > 1.8.3.2
>> >

Re: [PATCH 1/1] perf/x86: filter branches for PEBS event

[Peter Zijlstra]

On Thu, Mar 26, 2015 at 12:40:14PM -0700, Stephane Eranian wrote:
> You are addressing one of the problems of this routine. But I think
> there is a more serious issue which is not addressed here. The
> intel_shared_regs_constraints() assumes that the associated event is
> necessarily unconstrained:
> 
> __intel_shared_reg_get_constraints()
> {
>     struct event_constraint *c = &emptyconstraint;
>    ...
> }

emptyconstraint != unconstrained.

Note how that function only returns emptyconstraint if its rejecting the
event, otherwise it returns NULL such that we continue calling
x86_get_event_constraint().

> This is true for offcore_response, but for LBR this may not always be the case.
> I may want to use LBR on the L1D_PEND_MISS event and it would need to
> be on counter 2.

> But I believe that the current code could place it on counter 0 simply
> because you return if shared_reg_get_constraint() is successful, but
> it looks only at the LBR constraint not the event constraint. I think
> in the presence of LBR, you always need to call share_get_reg() and
> x86_get_event_constraint().

Which, I think it does.

Re: [PATCH 1/1] perf/x86: filter branches for PEBS event

[Peter Zijlstra]

On Thu, Mar 26, 2015 at 02:13:23PM -0400, kan.liang@intel.com wrote:
> This patch move intel_shared_regs_constraints for branch_reg ahead of
> intel_pebs_constraints.

Why not all shared regs?

> intel_shared_regs_constraints for branch_reg doesn't modify event->hw,
> so it's safe to be called before intel_pebs_constraints.
> intel_shared_regs_constraints for branch_reg also special case when it
> returns &emptyconstraint. It put constraints for extra_reg. This patch
> remove it. Because it will never get constraints for extra_reg if return
> is &emptyconstraint.

-ENOPARSE.

RE: [PATCH 1/1] perf/x86: filter branches for PEBS event

[Liang, Kan]

> On Thu, Mar 26, 2015 at 02:13:23PM -0400, kan.liang@intel.com wrote:
> > This patch move intel_shared_regs_constraints for branch_reg ahead of
> > intel_pebs_constraints.
> 
> Why not all shared regs?

Yes, all shared regs can also be moved ahead.
The patch is named for modifying the branch filter. I didn't want to change 
other codes. So I keep them unchanged.  
I will do it in next version.

> 
> > intel_shared_regs_constraints for branch_reg doesn't modify event->hw,
> > so it's safe to be called before intel_pebs_constraints.
> > intel_shared_regs_constraints for branch_reg also special case when it
> > returns &emptyconstraint. It put constraints for extra_reg. This patch
> > remove it. Because it will never get constraints for extra_reg if
> > return is &emptyconstraint.
> 
> -ENOPARSE.
Will remove the description, since it doesn't need in next version.

Thanks,
Kan

Re: [PATCH 1/1] perf/x86: filter branches for PEBS event

[Stephane Eranian]

On Fri, Mar 27, 2015 at 5:10 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Thu, Mar 26, 2015 at 12:40:14PM -0700, Stephane Eranian wrote:
>> You are addressing one of the problems of this routine. But I think
>> there is a more serious issue which is not addressed here. The
>> intel_shared_regs_constraints() assumes that the associated event is
>> necessarily unconstrained:
>>
>> __intel_shared_reg_get_constraints()
>> {
>>     struct event_constraint *c = &emptyconstraint;
>>    ...
>> }
>
> emptyconstraint != unconstrained.
>
> Note how that function only returns emptyconstraint if its rejecting the
> event, otherwise it returns NULL such that we continue calling
> x86_get_event_constraint().
>
Ah, yes, I had forgotten about that. Then everything is fine.

>> This is true for offcore_response, but for LBR this may not always be the case.
>> I may want to use LBR on the L1D_PEND_MISS event and it would need to
>> be on counter 2.
>
>> But I believe that the current code could place it on counter 0 simply
>> because you return if shared_reg_get_constraint() is successful, but
>> it looks only at the LBR constraint not the event constraint. I think
>> in the presence of LBR, you always need to call share_get_reg() and
>> x86_get_event_constraint().
>
> Which, I think it does.

Indeed.