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: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220616180623.1358843-1-namhyung@kernel.org

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index da759560eec5646f51ec8af94b2d561b786c3a2b..ee8b9ecdc03b752d0aa093f7d5446b01beb4e077 100644 (file)
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -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;

diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index d37629dbad72f72bc3920e3f22e4fa2752109c5c..0474ee362151f87fa007d2021e405309ac21563a 100644 (file)
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -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 */

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 80782cddb1dabf6f917b877acf262ead2cd911ae..4d8c335a07dbcbaf6a4f69b18b9c44377aeb6923 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -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));
        }

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index fb35b926024caeda34d6678f4bc98db6b70069b2..726132039c388eb03740e56555e522f8a97325b6 100644 (file)
--- 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();