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Commit 86e7972f authored by Wang Nan's avatar Wang Nan Committed by Ingo Molnar
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perf/ring_buffer: Introduce new ioctl options to pause and resume the ring-buffer 



Add new ioctl() to pause/resume ring-buffer output.

In some situations we want to read from the ring-buffer only when we
ensure nothing can write to the ring-buffer during reading. Without
this patch we have to turn off all events attached to this ring-buffer
to achieve this.

This patch is a prerequisite to enable overwrite support for the
perf ring-buffer support. Following commits will introduce new methods
support reading from overwrite ring buffer. Before reading, caller
must ensure the ring buffer is frozen, or the reading is unreliable.

Signed-off-by: default avatarWang Nan <wangnan0@huawei.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: <pi3orama@163.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: Zefan Li <lizefan@huawei.com>
Link: http://lkml.kernel.org/r/1459147292-239310-2-git-send-email-wangnan0@huawei.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 0a74c5b3

include/uapi/linux/perf_event.h

+1 −0
Original line number Diff line number Diff line
@@ -401,6 +401,7 @@ struct perf_event_attr { 
#define PERF_EVENT_IOC_SET_FILTER	_IOW('$', 6, char *)

#define PERF_EVENT_IOC_ID		_IOR('$', 7, __u64 *)

#define PERF_EVENT_IOC_SET_BPF		_IOW('$', 8, __u32)

#define PERF_EVENT_IOC_PAUSE_OUTPUT	_IOW('$', 9, __u32)



enum perf_event_ioc_flags {

	PERF_IOC_FLAG_GROUP		= 1U << 0,

kernel/events/core.c

+13 −0
Original line number Diff line number Diff line
@@ -4379,6 +4379,19 @@ static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned lon 
	case PERF_EVENT_IOC_SET_BPF:

		return perf_event_set_bpf_prog(event, arg);



	case PERF_EVENT_IOC_PAUSE_OUTPUT: {

		struct ring_buffer *rb;



		rcu_read_lock();

		rb = rcu_dereference(event->rb);

		if (!rb || !rb->nr_pages) {

			rcu_read_unlock();

			return -EINVAL;

		}

		rb_toggle_paused(rb, !!arg);

		rcu_read_unlock();

		return 0;

	}

	default:

		return -ENOTTY;

	}

kernel/events/internal.h

+9 −0
Original line number Diff line number Diff line
@@ -17,6 +17,7 @@ struct ring_buffer { 
#endif

	int				nr_pages;	/* nr of data pages  */

	int				overwrite;	/* can overwrite itself */

	int				paused;		/* can write into ring buffer */



	atomic_t			poll;		/* POLL_ for wakeups */
@@ -64,6 +65,14 @@ static inline void rb_free_rcu(struct rcu_head *rcu_head) 
	rb_free(rb);

}



static inline void rb_toggle_paused(struct ring_buffer *rb, bool pause)

{

	if (!pause && rb->nr_pages)

		rb->paused = 0;

	else

		rb->paused = 1;

}



extern struct ring_buffer *

rb_alloc(int nr_pages, long watermark, int cpu, int flags);

extern void perf_event_wakeup(struct perf_event *event);

kernel/events/ring_buffer.c

+11 −1
Original line number Diff line number Diff line
@@ -125,8 +125,11 @@ int perf_output_begin(struct perf_output_handle *handle, 
	if (unlikely(!rb))

		goto out;



	if (unlikely(!rb->nr_pages))

	if (unlikely(rb->paused)) {

		if (rb->nr_pages)

			local_inc(&rb->lost);

		goto out;

	}



	handle->rb    = rb;

	handle->event = event;
@@ -241,6 +244,13 @@ ring_buffer_init(struct ring_buffer *rb, long watermark, int flags) 


	INIT_LIST_HEAD(&rb->event_list);

	spin_lock_init(&rb->event_lock);



	/*

	 * perf_output_begin() only checks rb->paused, therefore

	 * rb->paused must be true if we have no pages for output.

	 */

	if (!rb->nr_pages)

		rb->paused = 1;

}



/*