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* [PATCH v2] perf/core: Add a new read format to get a number of lost samples
@ 2021-09-08 17:24 Namhyung Kim
  2021-09-10 21:42 ` Jiri Olsa
  0 siblings, 1 reply; 5+ messages in thread
From: Namhyung Kim @ 2021-09-08 17:24 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: Ingo Molnar, Arnaldo Carvalho de Melo, Jiri Olsa, Mark Rutland,
	Alexander Shishkin, LKML, Stephane Eranian, Andi Kleen,
	Ian Rogers, Michael Petlan

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: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 include/linux/perf_event.h      |  2 ++
 include/uapi/linux/perf_event.h |  5 ++++-
 kernel/events/core.c            | 22 +++++++++++++++++++---
 kernel/events/ring_buffer.c     |  5 ++++-
 4 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index f5a6a2f069ed..189a471fba42 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -756,6 +756,8 @@ 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;
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index bf8143505c49..f72008949ff0 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -299,6 +299,7 @@ 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;
@@ -306,6 +307,7 @@ 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
  * };
@@ -315,8 +317,9 @@ 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 */
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 0e125ae2fa92..8708325ee4a2 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1841,6 +1841,9 @@ 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);
@@ -5255,11 +5258,15 @@ 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_ID)
+		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_ID)
+			values[n++] = atomic64_read(&sub->lost_samples);
 	}
 
 	raw_spin_unlock_irqrestore(&ctx->lock, flags);
@@ -5316,7 +5323,7 @@ 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);
@@ -5326,6 +5333,8 @@ 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;
@@ -5664,6 +5673,7 @@ static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned lon
 
 		return perf_event_modify_attr(event,  &new_attr);
 	}
+
 	default:
 		return -ENOTTY;
 	}
@@ -6835,7 +6845,7 @@ 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);
@@ -6849,6 +6859,8 @@ 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));
 }
@@ -6859,7 +6871,7 @@ 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;
@@ -6877,6 +6889,8 @@ 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));
 
@@ -6890,6 +6904,8 @@ 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));
 	}
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 52868716ec35..727ca8f4caad 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -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();
-- 
2.33.0.309.g3052b89438-goog


^ permalink raw reply	[flat|nested] 5+ messages in thread

end of thread, other threads:[~2021-10-15  6:29 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-09-08 17:24 [PATCH v2] perf/core: Add a new read format to get a number of lost samples Namhyung Kim
2021-09-10 21:42 ` Jiri Olsa
2021-09-10 22:40   ` Namhyung Kim
2021-09-22 19:34     ` Namhyung Kim
2021-10-15  6:29       ` Namhyung Kim

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