Messages in this thread Patch in this message | | | From | Namhyung Kim <> | Subject | [PATCH] perf/core: Increase lost_samples count only for samples | Date | Fri, 2 Sep 2022 11:19:34 -0700 |
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The event->lost_samples count is intended to count (lost) sample records but it's also counted for non-sample records like PERF_RECORD_MMAP etc. This can be a problem when a sampling event tracks those side-band events together.
As overflow handler for user events only calls perf_output_begin_ {for,back}ward() before writing to the ring buffer, we can pass an additional flag to indicate that it's writing a sample record.
Fixes: 119a784c8127 ("perf/core: Add a new read format to get a number of lost samples") Signed-off-by: Namhyung Kim <namhyung@kernel.org> --- kernel/events/ring_buffer.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-)
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index 726132039c38..5f38ee4edbdb 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -149,7 +149,7 @@ static __always_inline int __perf_output_begin(struct perf_output_handle *handle, struct perf_sample_data *data, struct perf_event *event, unsigned int size, - bool backward) + bool backward, bool sample) { struct perf_buffer *rb; unsigned long tail, offset, head; @@ -174,7 +174,8 @@ __perf_output_begin(struct perf_output_handle *handle, if (unlikely(rb->paused)) { if (rb->nr_pages) { local_inc(&rb->lost); - atomic64_inc(&event->lost_samples); + if (sample) + atomic64_inc(&event->lost_samples); } goto out; } @@ -256,7 +257,8 @@ __perf_output_begin(struct perf_output_handle *handle, fail: local_inc(&rb->lost); - atomic64_inc(&event->lost_samples); + if (sample) + atomic64_inc(&event->lost_samples); perf_output_put_handle(handle); out: rcu_read_unlock(); @@ -268,14 +270,14 @@ int perf_output_begin_forward(struct perf_output_handle *handle, struct perf_sample_data *data, struct perf_event *event, unsigned int size) { - return __perf_output_begin(handle, data, event, size, false); + return __perf_output_begin(handle, data, event, size, false, true); } int perf_output_begin_backward(struct perf_output_handle *handle, struct perf_sample_data *data, struct perf_event *event, unsigned int size) { - return __perf_output_begin(handle, data, event, size, true); + return __perf_output_begin(handle, data, event, size, true, true); } int perf_output_begin(struct perf_output_handle *handle, @@ -284,7 +286,7 @@ int perf_output_begin(struct perf_output_handle *handle, { return __perf_output_begin(handle, data, event, size, - unlikely(is_write_backward(event))); + unlikely(is_write_backward(event)), false); } unsigned int perf_output_copy(struct perf_output_handle *handle, -- 2.37.2.789.g6183377224-goog
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