x86/perf/intel/cstate: Make cstate hotplug handling actually work

The current implementation aside of being an incomprehensible mess is broken.

  # cat /sys/bus/event_source/devices/cstate_core/cpumask
  0-17

That's on a quad socket machine with 72 physical cores! Qualitee stuff.

So it's not a surprise that event migration in case of CPU hotplug does not
work either.

  # perf stat -e cstate_core/c6-residency/ -C 1 sleep 60 &
  # echo 0 >/sys/devices/system/cpu/cpu1/online

Tracing cstate_pmu_event_update gives me:

 [001] cstate_pmu_event_update <-event_sched_out

After the fix it properly moves the event:

 [001] cstate_pmu_event_update <-event_sched_out
 [073] cstate_pmu_event_update <-__perf_event_read
 [073] cstate_pmu_event_update <-event_sched_out

The migration of pkg events does not work either. Not that I'm surprised.

I really could not be bothered to decode that loop mess and simply replaced it
by querying the proper cpumasks which give us the answer in a comprehensible
way.

This also requires to direct the event to the current active reader CPU in
cstate_pmu_event_init() otherwise the hotplug logic can't work.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[ Added event->cpu < 0 test to not explode]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Link: http://lkml.kernel.org/r/20160320185623.422519970@linutronix.deSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/events/intel/cstate.c

@@ -385,7 +385,7 @@ static ssize_t cstate_get_attr_cpumask(struct device *dev,
 static int cstate_pmu_event_init(struct perf_event *event)
 {
 	u64 cfg = event->attr.config;
-	int ret = 0;
+	int cpu;
 
 	if (event->attr.type != event->pmu->type)
 		return -ENOENT;
@@ -400,26 +400,36 @@ static int cstate_pmu_event_init(struct perf_event *event)
 	    event->attr.sample_period) /* no sampling */
 		return -EINVAL;
 
+	if (event->cpu < 0)
+		return -EINVAL;
+
 	if (event->pmu == &cstate_core_pmu) {
 		if (cfg >= PERF_CSTATE_CORE_EVENT_MAX)
 			return -EINVAL;
 		if (!core_msr[cfg].attr)
 			return -EINVAL;
 		event->hw.event_base = core_msr[cfg].msr;
+		cpu = cpumask_any_and(&cstate_core_cpu_mask,
+				      topology_sibling_cpumask(event->cpu));
 	} else if (event->pmu == &cstate_pkg_pmu) {
 		if (cfg >= PERF_CSTATE_PKG_EVENT_MAX)
 			return -EINVAL;
 		if (!pkg_msr[cfg].attr)
 			return -EINVAL;
 		event->hw.event_base = pkg_msr[cfg].msr;
-	} else
+		cpu = cpumask_any_and(&cstate_pkg_cpu_mask,
+				      topology_core_cpumask(event->cpu));
+	} else {
 		return -ENOENT;
+	}
+
+	if (cpu >= nr_cpu_ids)
+		return -ENODEV;
 
-	/* must be done before validate_group */
+	event->cpu = cpu;
 	event->hw.config = cfg;
 	event->hw.idx = -1;
-
-	return ret;
+	return 0;
 }
 
 static inline u64 cstate_pmu_read_counter(struct perf_event *event)
@@ -469,76 +479,59 @@ static int cstate_pmu_event_add(struct perf_event *event, int mode)
 	return 0;
 }
 
+/*
+ * Check if exiting cpu is the designated reader. If so migrate the
+ * events when there is a valid target available
+ */
 static void cstate_cpu_exit(int cpu)
 {
-	int i, id, target;
+	unsigned int target;
 
-	/* cpu exit for cstate core */
-	if (has_cstate_core) {
-		id = topology_core_id(cpu);
-		target = -1;
-
-		for_each_online_cpu(i) {
-			if (i == cpu)
-				continue;
-			if (id == topology_core_id(i)) {
-				target = i;
-				break;
-			}
-		}
-		if (cpumask_test_and_clear_cpu(cpu, &cstate_core_cpu_mask) && target >= 0)
+	if (has_cstate_core &&
+	    cpumask_test_and_clear_cpu(cpu, &cstate_core_cpu_mask)) {
+
+		target = cpumask_any_but(topology_sibling_cpumask(cpu), cpu);
+		/* Migrate events if there is a valid target */
+		if (target < nr_cpu_ids) {
 			cpumask_set_cpu(target, &cstate_core_cpu_mask);
-		WARN_ON(cpumask_empty(&cstate_core_cpu_mask));
-		if (target >= 0)
 			perf_pmu_migrate_context(&cstate_core_pmu, cpu, target);
 		}
-
-	/* cpu exit for cstate pkg */
-	if (has_cstate_pkg) {
-		id = topology_physical_package_id(cpu);
-		target = -1;
-
-		for_each_online_cpu(i) {
-			if (i == cpu)
-				continue;
-			if (id == topology_physical_package_id(i)) {
-				target = i;
-				break;
 	}
-		}
-		if (cpumask_test_and_clear_cpu(cpu, &cstate_pkg_cpu_mask) && target >= 0)
+
+	if (has_cstate_pkg &&
+	    cpumask_test_and_clear_cpu(cpu, &cstate_pkg_cpu_mask)) {
+
+		target = cpumask_any_but(topology_core_cpumask(cpu), cpu);
+		/* Migrate events if there is a valid target */
+		if (target < nr_cpu_ids) {
 			cpumask_set_cpu(target, &cstate_pkg_cpu_mask);
-		WARN_ON(cpumask_empty(&cstate_pkg_cpu_mask));
-		if (target >= 0)
 			perf_pmu_migrate_context(&cstate_pkg_pmu, cpu, target);
 		}
+	}
 }
 
 static void cstate_cpu_init(int cpu)
 {
-	int i, id;
+	unsigned int target;
 
-	/* cpu init for cstate core */
-	if (has_cstate_core) {
-		id = topology_core_id(cpu);
-		for_each_cpu(i, &cstate_core_cpu_mask) {
-			if (id == topology_core_id(i))
-				break;
-		}
-		if (i >= nr_cpu_ids)
+	/*
+	 * If this is the first online thread of that core, set it in
+	 * the core cpu mask as the designated reader.
+	 */
+	target = cpumask_any_and(&cstate_core_cpu_mask,
+				 topology_sibling_cpumask(cpu));
+
+	if (has_cstate_core && target >= nr_cpu_ids)
 		cpumask_set_cpu(cpu, &cstate_core_cpu_mask);
-	}
 
-	/* cpu init for cstate pkg */
-	if (has_cstate_pkg) {
-		id = topology_physical_package_id(cpu);
-		for_each_cpu(i, &cstate_pkg_cpu_mask) {
-			if (id == topology_physical_package_id(i))
-				break;
-		}
-		if (i >= nr_cpu_ids)
+	/*
+	 * If this is the first online thread of that package, set it
+	 * in the package cpu mask as the designated reader.
+	 */
+	target = cpumask_any_and(&cstate_pkg_cpu_mask,
+				 topology_core_cpumask(cpu));
+	if (has_cstate_pkg && target >= nr_cpu_ids)
 		cpumask_set_cpu(cpu, &cstate_pkg_cpu_mask);
-	}
 }
 
 static int cstate_cpu_notifier(struct notifier_block *self,
@@ -547,24 +540,15 @@ static int cstate_cpu_notifier(struct notifier_block *self,
 	unsigned int cpu = (long)hcpu;
 
 	switch (action & ~CPU_TASKS_FROZEN) {
-	case CPU_UP_PREPARE:
-		break;
 	case CPU_STARTING:
 		cstate_cpu_init(cpu);
 		break;
-	case CPU_UP_CANCELED:
-	case CPU_DYING:
-		break;
-	case CPU_ONLINE:
-	case CPU_DEAD:
-		break;
 	case CPU_DOWN_PREPARE:
 		cstate_cpu_exit(cpu);
 		break;
 	default:
 		break;
 	}
-
 	return NOTIFY_OK;
 }