From: Namhyung Kim <namhyung@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Jiri Olsa <jolsa@redhat.com>, Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
LKML <linux-kernel@vger.kernel.org>,
Stephane Eranian <eranian@google.com>,
Andi Kleen <ak@linux.intel.com>, Ian Rogers <irogers@google.com>,
gmx@google.com
Subject: [RFC] perf/core: Add an ioctl to get a number of lost samples
Date: Tue, 10 Aug 2021 23:21:35 -0700 [thread overview]
Message-ID: <20210811062135.1332927-1-namhyung@kernel.org> (raw)
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_EVENT_IOC_LOST_SAMPLES to
retrieve it from userspace.
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
include/linux/perf_event.h | 2 ++
include/uapi/linux/perf_event.h | 1 +
kernel/events/core.c | 9 +++++++++
kernel/events/ring_buffer.c | 5 ++++-
4 files changed, 16 insertions(+), 1 deletion(-)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index f5a6a2f069ed..44d72079c77a 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;
+ atomic_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..24397799127d 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -505,6 +505,7 @@ struct perf_event_query_bpf {
#define PERF_EVENT_IOC_PAUSE_OUTPUT _IOW('$', 9, __u32)
#define PERF_EVENT_IOC_QUERY_BPF _IOWR('$', 10, struct perf_event_query_bpf *)
#define PERF_EVENT_IOC_MODIFY_ATTRIBUTES _IOW('$', 11, struct perf_event_attr *)
+#define PERF_EVENT_IOC_LOST_SAMPLES _IOR('$', 12, __u64 *)
enum perf_event_ioc_flags {
PERF_IOC_FLAG_GROUP = 1U << 0,
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 0e125ae2fa92..a4d6736b6594 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5664,6 +5664,15 @@ static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned lon
return perf_event_modify_attr(event, &new_attr);
}
+
+ case PERF_EVENT_IOC_LOST_SAMPLES: {
+ u64 lost = atomic_read(&event->lost_samples);
+
+ if (copy_to_user((void __user *)arg, &lost, sizeof(lost)))
+ return -EFAULT;
+ return 0;
+ }
+
default:
return -ENOTTY;
}
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 52868716ec35..06d7dacb05da 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);
+ atomic_inc(&event->lost_samples);
+ }
goto out;
}
@@ -254,6 +256,7 @@ __perf_output_begin(struct perf_output_handle *handle,
fail:
local_inc(&rb->lost);
+ atomic_inc(&event->lost_samples);
perf_output_put_handle(handle);
out:
rcu_read_unlock();
--
2.32.0.605.g8dce9f2422-goog
next reply other threads:[~2021-08-11 6:21 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-11 6:21 Namhyung Kim [this message]
2021-08-11 13:12 ` [RFC] perf/core: Add an ioctl to get a number of lost samples Andi Kleen
2021-08-11 15:04 ` Jiri Olsa
2021-08-11 19:33 ` Stephane Eranian
2021-08-11 19:57 ` Jiri Olsa
2021-08-11 20:57 ` Namhyung Kim
2021-08-11 23:57 ` Stephane Eranian
2021-08-11 20:54 ` Namhyung Kim
2021-08-24 14:02 ` Peter Zijlstra
2021-08-24 17:55 ` Namhyung Kim
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