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.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/events/intel/cstate.c b/arch/x86/events/intel/cstate.c
index 7946c4231169ff81ed2c22cd538cdf289e8930f2..5c2f55fe142ad64474be08e111723821d4cde6c4 100644 (file)
--- a/arch/x86/events/intel/cstate.c
+++ b/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;
+       }
 
-       /* must be done before validate_group */
+       if (cpu >= nr_cpu_ids)
+               return -ENODEV;
+
+       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)
@@ -469,102 +479,76 @@ 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)
-                       cpumask_set_cpu(cpu, &cstate_core_cpu_mask);
-       }
+       /*
+        * 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));
 
-       /* 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)
-                       cpumask_set_cpu(cpu, &cstate_pkg_cpu_mask);
-       }
+       if (has_cstate_core && target >= nr_cpu_ids)
+               cpumask_set_cpu(cpu, &cstate_core_cpu_mask);
+
+       /*
+        * 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,
-                                 unsigned long action, void *hcpu)
+                              unsigned long action, void *hcpu)
 {
        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;
 }