Commit 119a784c authored by Namhyung Kim's avatar Namhyung Kim Committed by Peter Zijlstra
Browse files

perf/core: Add a new read format to get a number of lost samples 



Sometimes we want to know an accurate number of samples even if it's
lost.  Currenlty PERF_RECORD_LOST is generated for a ring-buffer which
might be shared with other events.  So it's hard to know per-event
lost count.

Add event->lost_samples field and PERF_FORMAT_LOST to retrieve it from
userspace.

Original-patch-by: default avatarJiri Olsa <jolsa@redhat.com>
Signed-off-by: default avatarNamhyung Kim <namhyung@kernel.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220616180623.1358843-1-namhyung@kernel.org
parent f0fe9f3c

include/linux/perf_event.h

+2 −0
Original line number Diff line number Diff line
@@ -759,6 +759,8 @@ struct perf_event { 
	struct pid_namespace		*ns;

	u64				id;



	atomic64_t			lost_samples;



	u64				(*clock)(void);

	perf_overflow_handler_t		overflow_handler;

	void				*overflow_handler_context;

include/uapi/linux/perf_event.h

+4 −1
Original line number Diff line number Diff line
@@ -301,6 +301,7 @@ enum { 
 *	  { u64		time_enabled; } && PERF_FORMAT_TOTAL_TIME_ENABLED

 *	  { u64		time_running; } && PERF_FORMAT_TOTAL_TIME_RUNNING

 *	  { u64		id;           } && PERF_FORMAT_ID

 *	  { u64		lost;         } && PERF_FORMAT_LOST

 *	} && !PERF_FORMAT_GROUP

 *

 *	{ u64		nr;
@@ -308,6 +309,7 @@ enum { 
 *	  { u64		time_running; } && PERF_FORMAT_TOTAL_TIME_RUNNING

 *	  { u64		value;

 *	    { u64	id;           } && PERF_FORMAT_ID

 *	    { u64	lost;         } && PERF_FORMAT_LOST

 *	  }		cntr[nr];

 *	} && PERF_FORMAT_GROUP

 * };
@@ -317,8 +319,9 @@ enum perf_event_read_format { 
	PERF_FORMAT_TOTAL_TIME_RUNNING		= 1U << 1,

	PERF_FORMAT_ID				= 1U << 2,

	PERF_FORMAT_GROUP			= 1U << 3,

	PERF_FORMAT_LOST			= 1U << 4,



	PERF_FORMAT_MAX = 1U << 4,		/* non-ABI */

	PERF_FORMAT_MAX = 1U << 5,		/* non-ABI */

};



#define PERF_ATTR_SIZE_VER0	64	/* sizeof first published struct */

kernel/events/core.c

+18 −3
Original line number Diff line number Diff line
@@ -1819,6 +1819,9 @@ static void __perf_event_read_size(struct perf_event *event, int nr_siblings) 
	if (event->attr.read_format & PERF_FORMAT_ID)

		entry += sizeof(u64);



	if (event->attr.read_format & PERF_FORMAT_LOST)

		entry += sizeof(u64);



	if (event->attr.read_format & PERF_FORMAT_GROUP) {

		nr += nr_siblings;

		size += sizeof(u64);
@@ -5260,11 +5263,15 @@ static int __perf_read_group_add(struct perf_event *leader, 
	values[n++] += perf_event_count(leader);

	if (read_format & PERF_FORMAT_ID)

		values[n++] = primary_event_id(leader);

	if (read_format & PERF_FORMAT_LOST)

		values[n++] = atomic64_read(&leader->lost_samples);



	for_each_sibling_event(sub, leader) {

		values[n++] += perf_event_count(sub);

		if (read_format & PERF_FORMAT_ID)

			values[n++] = primary_event_id(sub);

		if (read_format & PERF_FORMAT_LOST)

			values[n++] = atomic64_read(&sub->lost_samples);

	}



	raw_spin_unlock_irqrestore(&ctx->lock, flags);
@@ -5321,7 +5328,7 @@ static int perf_read_one(struct perf_event *event, 
				 u64 read_format, char __user *buf)

{

	u64 enabled, running;

	u64 values[4];

	u64 values[5];

	int n = 0;



	values[n++] = __perf_event_read_value(event, &enabled, &running);
@@ -5331,6 +5338,8 @@ static int perf_read_one(struct perf_event *event, 
		values[n++] = running;

	if (read_format & PERF_FORMAT_ID)

		values[n++] = primary_event_id(event);

	if (read_format & PERF_FORMAT_LOST)

		values[n++] = atomic64_read(&event->lost_samples);



	if (copy_to_user(buf, values, n * sizeof(u64)))

		return -EFAULT;
@@ -6858,7 +6867,7 @@ static void perf_output_read_one(struct perf_output_handle *handle, 
				 u64 enabled, u64 running)

{

	u64 read_format = event->attr.read_format;

	u64 values[4];

	u64 values[5];

	int n = 0;



	values[n++] = perf_event_count(event);
@@ -6872,6 +6881,8 @@ static void perf_output_read_one(struct perf_output_handle *handle, 
	}

	if (read_format & PERF_FORMAT_ID)

		values[n++] = primary_event_id(event);

	if (read_format & PERF_FORMAT_LOST)

		values[n++] = atomic64_read(&event->lost_samples);



	__output_copy(handle, values, n * sizeof(u64));

}
@@ -6882,7 +6893,7 @@ static void perf_output_read_group(struct perf_output_handle *handle, 
{

	struct perf_event *leader = event->group_leader, *sub;

	u64 read_format = event->attr.read_format;

	u64 values[5];

	u64 values[6];

	int n = 0;



	values[n++] = 1 + leader->nr_siblings;
@@ -6900,6 +6911,8 @@ static void perf_output_read_group(struct perf_output_handle *handle, 
	values[n++] = perf_event_count(leader);

	if (read_format & PERF_FORMAT_ID)

		values[n++] = primary_event_id(leader);

	if (read_format & PERF_FORMAT_LOST)

		values[n++] = atomic64_read(&leader->lost_samples);



	__output_copy(handle, values, n * sizeof(u64));
@@ -6913,6 +6926,8 @@ static void perf_output_read_group(struct perf_output_handle *handle, 
		values[n++] = perf_event_count(sub);

		if (read_format & PERF_FORMAT_ID)

			values[n++] = primary_event_id(sub);

		if (read_format & PERF_FORMAT_LOST)

			values[n++] = atomic64_read(&sub->lost_samples);



		__output_copy(handle, values, n * sizeof(u64));

	}

kernel/events/ring_buffer.c

+4 −1
Original line number Diff line number Diff line
@@ -172,8 +172,10 @@ __perf_output_begin(struct perf_output_handle *handle, 
		goto out;



	if (unlikely(rb->paused)) {

		if (rb->nr_pages)

		if (rb->nr_pages) {

			local_inc(&rb->lost);

			atomic64_inc(&event->lost_samples);

		}

		goto out;

	}
@@ -254,6 +256,7 @@ __perf_output_begin(struct perf_output_handle *handle, 


fail:

	local_inc(&rb->lost);

	atomic64_inc(&event->lost_samples);

	perf_output_put_handle(handle);

out:

	rcu_read_unlock();