perf/x86/amd: Cleanup Fam10h NB event constraints

Avoid allocating the AMD NB event constraints data structure when not
needed. This gets rid of x86_max_cores usage and avoids allocating
this on AMD Core Perfctr supporting hardware (which has separate MSRs
for NB events).

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: aherrmann@suse.com
Cc: Rui Huang <ray.huang@amd.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: jencce.kernel@gmail.com
Link: http://lkml.kernel.org/r/20160320124629.GY6375@twins.programming.kicks-ass.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/events/amd/core.c

@@ -369,7 +369,7 @@ static int amd_pmu_cpu_prepare(int cpu)
 
 	WARN_ON_ONCE(cpuc->amd_nb);
 
-	if (boot_cpu_data.x86_max_cores < 2)
+	if (!x86_pmu.amd_nb_constraints)
 		return NOTIFY_OK;
 
 	cpuc->amd_nb = amd_alloc_nb(cpu);
@@ -388,7 +388,7 @@ static void amd_pmu_cpu_starting(int cpu)
 
 	cpuc->perf_ctr_virt_mask = AMD64_EVENTSEL_HOSTONLY;
 
-	if (boot_cpu_data.x86_max_cores < 2)
+	if (!x86_pmu.amd_nb_constraints)
 		return;
 
 	nb_id = amd_get_nb_id(cpu);
@@ -414,7 +414,7 @@ static void amd_pmu_cpu_dead(int cpu)
 {
 	struct cpu_hw_events *cpuhw;
 
-	if (boot_cpu_data.x86_max_cores < 2)
+	if (!x86_pmu.amd_nb_constraints)
 		return;
 
 	cpuhw = &per_cpu(cpu_hw_events, cpu);
@@ -648,6 +648,8 @@ static __initconst const struct x86_pmu amd_pmu = {
 	.cpu_prepare		= amd_pmu_cpu_prepare,
 	.cpu_starting		= amd_pmu_cpu_starting,
 	.cpu_dead		= amd_pmu_cpu_dead,
+
+	.amd_nb_constraints	= 1,
 };
 
 static int __init amd_core_pmu_init(void)
@@ -674,6 +676,11 @@ static int __init amd_core_pmu_init(void)
 	x86_pmu.eventsel	= MSR_F15H_PERF_CTL;
 	x86_pmu.perfctr		= MSR_F15H_PERF_CTR;
 	x86_pmu.num_counters	= AMD64_NUM_COUNTERS_CORE;
+	/*
+	 * AMD Core perfctr has separate MSRs for the NB events, see
+	 * the amd/uncore.c driver.
+	 */
+	x86_pmu.amd_nb_constraints = 0;
 
 	pr_cont("core perfctr, ");
 	return 0;
@@ -693,6 +700,14 @@ __init int amd_pmu_init(void)
 	if (ret)
 		return ret;
 
+	if (num_possible_cpus() == 1) {
+		/*
+		 * No point in allocating data structures to serialize
+		 * against other CPUs, when there is only the one CPU.
+		 */
+		x86_pmu.amd_nb_constraints = 0;
+	}
+
 	/* Events are common for all AMDs */
 	memcpy(hw_cache_event_ids, amd_hw_cache_event_ids,
 	       sizeof(hw_cache_event_ids));

arch/x86/events/perf_event.h

@@ -607,6 +607,11 @@ struct x86_pmu {
 	 */
 	atomic_t	lbr_exclusive[x86_lbr_exclusive_max];
 
+	/*
+	 * AMD bits
+	 */
+	unsigned int	amd_nb_constraints : 1;
+
 	/*
 	 * Extra registers for events
 	 */