[PATCH 4/9] perf/x86: special case per-cpu core misc PMU events

[kan.liang@intel.com]

From: Kan Liang <kan.liang@intel.com>

This patch special case per-cpu core_misc PMU events and allow them to
be part of any hardware/software group for system-wide monitoring.
An useful example would be to include the ASTATE/MSTATE event in a
sampling group. This can be used to calculate the frequency during each
sampling period, and track it over time.

A new context type (perf_free_context) is introduced to indicate these
per-cpu core misc PMU events. They are
 - Free running counter
 - Don't have any state to switch on context switch and never fails
   to schedule
 - No sampling support
 - Only support system-wide monitoring
 - per-cpu
We also defined a new PERF event type PERF_TYPE_CORE_MISC_FREE for them.

It's safe to mix cpu PMU events and CORE_MISC_FREE events in a group.
Because when cpu PMU events disable/enable, we can disable/enable
them at the same time without failure.

Since there is no sampling support for these events. They are only
available for group reading and system-wide monitoring.

Signed-off-by: Kan Liang <kan.liang@intel.com>
---
 arch/x86/kernel/cpu/perf_event_intel_core_misc.c |  8 +++++---
 include/linux/perf_event.h                       | 10 ++++++++++
 include/linux/sched.h                            |  1 +
 include/uapi/linux/perf_event.h                  |  1 +
 kernel/events/core.c                             |  9 +++++++++
 5 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel_core_misc.c b/arch/x86/kernel/cpu/perf_event_intel_core_misc.c
index 4efe842..dad4495 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_core_misc.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_core_misc.c
@@ -889,7 +889,6 @@ static void __init core_misc_pmus_register(void)
 
 		type->pmu = (struct pmu) {
 			.attr_groups	= type->pmu_group,
-			.task_ctx_nr	= perf_invalid_context,
 			.event_init	= core_misc_pmu_event_init,
 			.add		= core_misc_pmu_event_add, /* must have */
 			.del		= core_misc_pmu_event_del, /* must have */
@@ -902,9 +901,12 @@ static void __init core_misc_pmus_register(void)
 		if (type->type == perf_intel_core_misc_thread) {
 			type->pmu.pmu_disable = (void *) intel_core_misc_pmu_disable;
 			type->pmu.pmu_enable = (void *) intel_core_misc_pmu_enable;
+			type->pmu.task_ctx_nr = perf_free_context;
+			err = perf_pmu_register(&type->pmu, type->name, PERF_TYPE_CORE_MISC_FREE);
+		} else {
+			type->pmu.task_ctx_nr = perf_invalid_context;
+			err = perf_pmu_register(&type->pmu, type->name, -1);
 		}
-
-		err = perf_pmu_register(&type->pmu, type->name, -1);
 		if (WARN_ON(err))
 			pr_info("Failed to register PMU %s error %d\n",
 				type->pmu.name, err);
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index fea0ddf..3538f1c 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -773,6 +773,16 @@ static inline int is_hardware_event(struct perf_event *event)
 	return event->pmu->task_ctx_nr == perf_hw_context;
 }
 
+static inline int is_free_event(struct perf_event *event)
+{
+	return event->pmu->task_ctx_nr == perf_free_context;
+}
+
+static inline int has_context_event(struct perf_event *event)
+{
+	return event->pmu->task_ctx_nr > perf_invalid_context;
+}
+
 extern struct static_key perf_swevent_enabled[PERF_COUNT_SW_MAX];
 
 extern void ___perf_sw_event(u32, u64, struct pt_regs *, u64);
diff --git a/include/linux/sched.h b/include/linux/sched.h
index ae21f15..717f492 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1335,6 +1335,7 @@ union rcu_special {
 struct rcu_node;
 
 enum perf_event_task_context {
+	perf_free_context = -2,
 	perf_invalid_context = -1,
 	perf_hw_context = 0,
 	perf_sw_context,
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index d97f84c..232b674 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -32,6 +32,7 @@ enum perf_type_id {
 	PERF_TYPE_HW_CACHE			= 3,
 	PERF_TYPE_RAW				= 4,
 	PERF_TYPE_BREAKPOINT			= 5,
+	PERF_TYPE_CORE_MISC_FREE		= 6,
 
 	PERF_TYPE_MAX,				/* non-ABI */
 };
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 9077867..995b436 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -8019,6 +8019,15 @@ SYSCALL_DEFINE5(perf_event_open,
 	}
 
 	/*
+	 * Special case per-cpu free counter events and allow them to be part of
+	 * any hardware/software group for system-wide monitoring.
+	 */
+	if (group_leader && !task &&
+	    is_free_event(event) &&
+	    has_context_event(group_leader))
+		pmu = group_leader->pmu;
+
+	/*
 	 * Get the target context (task or percpu):
 	 */
 	ctx = find_get_context(pmu, task, event);
-- 
1.8.3.1