[RFC][PATCH 6/8] perf/x86: Clear ->event_constraint[] on put

[Peter Zijlstra]

The current code unconditionally clears cpuc->event_constraint[i]
before calling get_event_constraints(.idx=i). The only site that cares
is intel_get_event_constraints() where the c1 load will always be
NULL.

However, always calling get_event_constraints() on all events is
wastefull, most times it will return the exact same result. Therefore
retain the logic in intel_get_event_constraints() and change the
generic code to only clear the constraint on put.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 arch/x86/events/core.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -858,7 +858,6 @@ int x86_schedule_events(struct cpu_hw_ev
 		x86_pmu.start_scheduling(cpuc);
 
 	for (i = 0, wmin = X86_PMC_IDX_MAX, wmax = 0; i < n; i++) {
-		cpuc->event_constraint[i] = NULL;
 		c = x86_pmu.get_event_constraints(cpuc, i, cpuc->event_list[i]);
 		cpuc->event_constraint[i] = c;
 
@@ -941,6 +940,8 @@ int x86_schedule_events(struct cpu_hw_ev
 			 */
 			if (x86_pmu.put_event_constraints)
 				x86_pmu.put_event_constraints(cpuc, e);
+
+			cpuc->event_constraint[i] = NULL;
 		}
 	}
 
@@ -1404,6 +1405,7 @@ static void x86_pmu_del(struct perf_even
 		cpuc->event_list[i-1] = cpuc->event_list[i];
 		cpuc->event_constraint[i-1] = cpuc->event_constraint[i];
 	}
+	cpuc->event_constraint[i-1] = NULL;
 	--cpuc->n_events;
 
 	perf_event_update_userpage(event);