linux-kernel - [RFC][PATCH 3/8] perf/x86: Simplify x86_pmu.get

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Date:   Thu, 14 Mar 2019 14:01:16 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     mingo@...nel.org, eranian@...gle.com, jolsa@...hat.com
Cc:     linux-kernel@...r.kernel.org, tonyj@...e.com,
        nelson.dsouza@...el.com, peterz@...radead.org
Subject: [RFC][PATCH 3/8] perf/x86: Simplify x86_pmu.get_constraints() interface

There is a special case for validate_events() where we'll call
x86_pmu.get_constraints(.idx=-1). It's purpose, up until recent, seems
to be to avoid taking a previous constraint from
cpuc->event_constraint[] in intel_get_event_constraints().

(I could not find any other get_event_constraints() implementation
using @idx)

However, since that cpuc is freshly allocated, that array will in fact
be initialized with NULL pointers, achieving the very same effect.

Therefore remove this exception.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/events/core.c       |    2 +-
 arch/x86/events/intel/core.c |    8 +++-----
 2 files changed, 4 insertions(+), 6 deletions(-)

--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2031,7 +2031,7 @@ static int validate_event(struct perf_ev
 	if (IS_ERR(fake_cpuc))
 		return PTR_ERR(fake_cpuc);
 
-	c = x86_pmu.get_event_constraints(fake_cpuc, -1, event);
+	c = x86_pmu.get_event_constraints(fake_cpuc, 0, event);
 
 	if (!c || !c->weight)
 		ret = -EINVAL;
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -2931,11 +2931,9 @@ static struct event_constraint *
 intel_get_event_constraints(struct cpu_hw_events *cpuc, int idx,
 			    struct perf_event *event)
 {
-	struct event_constraint *c1 = NULL;
-	struct event_constraint *c2;
+	struct event_constraint *c1, *c2;
 
-	if (idx >= 0) /* fake does < 0 */
-		c1 = cpuc->event_constraint[idx];
+	c1 = cpuc->event_constraint[idx];
 
 	/*
 	 * first time only
@@ -3410,7 +3408,7 @@ tfa_get_event_constraints(struct cpu_hw_
 	/*
 	 * Without TFA we must not use PMC3.
 	 */
-	if (!allow_tsx_force_abort && test_bit(3, c->idxmsk) && idx >= 0) {
+	if (!allow_tsx_force_abort && test_bit(3, c->idxmsk)) {
 		c = dyn_constraint(cpuc, c, idx);
 		c->idxmsk64 &= ~(1ULL << 3);
 		c->weight--;