[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) <pet...@infradead.org>
---
 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);