Commit ffe8690c authored by Kaixu Xia's avatar Kaixu Xia Committed by David S. Miller
Browse files

perf: add the necessary core perf APIs when accessing events counters in eBPF programs 



This patch add three core perf APIs:
 - perf_event_attrs(): export the struct perf_event_attr from struct
   perf_event;
 - perf_event_get(): get the struct perf_event from the given fd;
 - perf_event_read_local(): read the events counters active on the
   current CPU;
These APIs are needed when accessing events counters in eBPF programs.

The API perf_event_read_local() comes from Peter and I add the
corresponding SOB.

Signed-off-by: default avatarKaixu Xia <xiakaixu@huawei.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent f1d5ca43

include/linux/perf_event.h

+10 −0
Original line number Diff line number Diff line
@@ -641,6 +641,8 @@ extern int perf_event_init_task(struct task_struct *child); 
extern void perf_event_exit_task(struct task_struct *child);

extern void perf_event_free_task(struct task_struct *task);

extern void perf_event_delayed_put(struct task_struct *task);

extern struct perf_event *perf_event_get(unsigned int fd);

extern const struct perf_event_attr *perf_event_attrs(struct perf_event *event);

extern void perf_event_print_debug(void);

extern void perf_pmu_disable(struct pmu *pmu);

extern void perf_pmu_enable(struct pmu *pmu);
@@ -659,6 +661,7 @@ perf_event_create_kernel_counter(struct perf_event_attr *attr, 
				void *context);

extern void perf_pmu_migrate_context(struct pmu *pmu,

				int src_cpu, int dst_cpu);

extern u64 perf_event_read_local(struct perf_event *event);

extern u64 perf_event_read_value(struct perf_event *event,

				 u64 *enabled, u64 *running);
@@ -979,6 +982,12 @@ static inline int perf_event_init_task(struct task_struct *child) { return 0; } 
static inline void perf_event_exit_task(struct task_struct *child)	{ }

static inline void perf_event_free_task(struct task_struct *task)	{ }

static inline void perf_event_delayed_put(struct task_struct *task)	{ }

static inline struct perf_event *perf_event_get(unsigned int fd)	{ return ERR_PTR(-EINVAL); }

static inline const struct perf_event_attr *perf_event_attrs(struct perf_event *event)

{

	return ERR_PTR(-EINVAL);

}

static inline u64 perf_event_read_local(struct perf_event *event)	{ return -EINVAL; }

static inline void perf_event_print_debug(void)				{ }

static inline int perf_event_task_disable(void)				{ return -EINVAL; }

static inline int perf_event_task_enable(void)				{ return -EINVAL; }
@@ -1011,6 +1020,7 @@ static inline void perf_event_enable(struct perf_event *event) { } 
static inline void perf_event_disable(struct perf_event *event)		{ }

static inline int __perf_event_disable(void *info)			{ return -1; }

static inline void perf_event_task_tick(void)				{ }

static inline int perf_event_release_kernel(struct perf_event *event)	{ return 0; }

#endif



#if defined(CONFIG_PERF_EVENTS) && defined(CONFIG_NO_HZ_FULL)

kernel/events/core.c

+78 −0
Original line number Diff line number Diff line
@@ -3212,6 +3212,59 @@ static inline u64 perf_event_count(struct perf_event *event) 
	return __perf_event_count(event);

}



/*

 * NMI-safe method to read a local event, that is an event that

 * is:

 *   - either for the current task, or for this CPU

 *   - does not have inherit set, for inherited task events

 *     will not be local and we cannot read them atomically

 *   - must not have a pmu::count method

 */

u64 perf_event_read_local(struct perf_event *event)

{

	unsigned long flags;

	u64 val;



	/*

	 * Disabling interrupts avoids all counter scheduling (context

	 * switches, timer based rotation and IPIs).

	 */

	local_irq_save(flags);



	/* If this is a per-task event, it must be for current */

	WARN_ON_ONCE((event->attach_state & PERF_ATTACH_TASK) &&

		     event->hw.target != current);



	/* If this is a per-CPU event, it must be for this CPU */

	WARN_ON_ONCE(!(event->attach_state & PERF_ATTACH_TASK) &&

		     event->cpu != smp_processor_id());



	/*

	 * It must not be an event with inherit set, we cannot read

	 * all child counters from atomic context.

	 */

	WARN_ON_ONCE(event->attr.inherit);



	/*

	 * It must not have a pmu::count method, those are not

	 * NMI safe.

	 */

	WARN_ON_ONCE(event->pmu->count);



	/*

	 * If the event is currently on this CPU, its either a per-task event,

	 * or local to this CPU. Furthermore it means its ACTIVE (otherwise

	 * oncpu == -1).

	 */

	if (event->oncpu == smp_processor_id())

		event->pmu->read(event);



	val = local64_read(&event->count);

	local_irq_restore(flags);



	return val;

}



static u64 perf_event_read(struct perf_event *event)

{

	/*
@@ -8574,6 +8627,31 @@ void perf_event_delayed_put(struct task_struct *task) 
		WARN_ON_ONCE(task->perf_event_ctxp[ctxn]);

}



struct perf_event *perf_event_get(unsigned int fd)

{

	int err;

	struct fd f;

	struct perf_event *event;



	err = perf_fget_light(fd, &f);

	if (err)

		return ERR_PTR(err);



	event = f.file->private_data;

	atomic_long_inc(&event->refcount);

	fdput(f);



	return event;

}



const struct perf_event_attr *perf_event_attrs(struct perf_event *event)

{

	if (!event)

		return ERR_PTR(-EINVAL);



	return &event->attr;

}



/*

 * inherit a event from parent task to child task:

 */

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