perf tools: handle PERF_RECORD_LOST_SAMPLES

This patch modifies the perf tool to handle the new RECORD type,
PERF_RECORD_LOST_SAMPLES.

The number of lost-sample events is stored in
.nr_events[PERF_RECORD_LOST_SAMPLES]. The exact number of samples
which the kernel dropped is stored in total_lost_samples.

When the percentage of dropped samples is greater than 5%, a warning
is printed.

Here are some examples:

Eg 1, Recording different frequently-occurring events is safe with the
      patch. Only a very low drop rate is associated with such actions.

$ perf record -e '{cycles:p,instructions:p}' -c 20003 --no-time ~/tchain ~/tchain

$ perf report -D | tail
          SAMPLE events:     120243
           MMAP2 events:          5
    LOST_SAMPLES events:         24
  FINISHED_ROUND events:         15
cycles:p stats:
           TOTAL events:      59348
          SAMPLE events:      59348
instructions:p stats:
           TOTAL events:      60895
          SAMPLE events:      60895

$ perf report --stdio --group
 # To display the perf.data header info, please use --header/--header-only options.
 #
 #
 # Total Lost Samples: 24
 #
 # Samples: 120K of event 'anon group { cycles:p, instructions:p }'
 # Event count (approx.): 24048600000
 #
 #         Overhead  Command      Shared Object     Symbol
 # ................  ...........  ................
 ..................................
 #
    99.74%  99.86%  tchain_edit  tchain_edit       [.] f3
     0.09%   0.02%  tchain_edit  tchain_edit       [.] f2
     0.04%   0.00%  tchain_edit  [kernel.vmlinux]  [k] ixgbe_read_reg

Eg 2, Recording the same thing multiple times can lead to high drop
      rate, but it is not a useful configuration.

$ perf record -e '{cycles:p,cycles:p}' -c 20003 --no-time ~/tchain
Warning: Processed 600592 samples and lost 99.73% samples!
[perf record: Woken up 148 times to write data]
[perf record: Captured and wrote 36.922 MB perf.data (1206322 samples)]
[perf record: Woken up 1 times to write data]
[perf record: Captured and wrote 0.121 MB perf.data (1629 samples)]

Signed-off-by: Kan Liang <kan.liang@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: acme@infradead.org
Cc: eranian@google.com
Link: http://lkml.kernel.org/r/1431285195-14269-9-git-send-email-kan.liang@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 19 insertions, 0 deletions

diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 39fe09d5a87e..88d87bf3049f 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -325,6 +325,8 @@ void perf_tool__fill_defaults(struct perf_tool *tool)
 		tool->exit = process_event_stub;
 	if (tool->lost == NULL)
 		tool->lost = perf_event__process_lost;
+	if (tool->lost_samples == NULL)
+		tool->lost_samples = perf_event__process_lost_samples;
 	if (tool->aux == NULL)
 		tool->aux = perf_event__process_aux;
 	if (tool->itrace_start == NULL)
@@ -606,6 +608,7 @@ static perf_event__swap_op perf_event__swap_ops[] = {
 	[PERF_RECORD_SAMPLE]		  = perf_event__all64_swap,
 	[PERF_RECORD_AUX]		  = perf_event__aux_swap,
 	[PERF_RECORD_ITRACE_START]	  = perf_event__itrace_start_swap,
+	[PERF_RECORD_LOST_SAMPLES]	  = perf_event__all64_swap,
 	[PERF_RECORD_HEADER_ATTR]	  = perf_event__hdr_attr_swap,
 	[PERF_RECORD_HEADER_EVENT_TYPE]	  = perf_event__event_type_swap,
 	[PERF_RECORD_HEADER_TRACING_DATA] = perf_event__tracing_data_swap,
@@ -1049,6 +1052,10 @@ static int machines__deliver_event(struct machines *machines,
 		if (tool->lost == perf_event__process_lost)
 			evlist->stats.total_lost += event->lost.lost;
 		return tool->lost(tool, event, sample, machine);
+	case PERF_RECORD_LOST_SAMPLES:
+		if (tool->lost_samples == perf_event__process_lost_samples)
+			evlist->stats.total_lost_samples += event->lost_samples.lost;
+		return tool->lost_samples(tool, event, sample, machine);
 	case PERF_RECORD_READ:
 		return tool->read(tool, event, sample, evsel, machine);
 	case PERF_RECORD_THROTTLE:
@@ -1286,6 +1293,18 @@ static void perf_session__warn_about_errors(const struct perf_session *session)
 			    stats->nr_events[PERF_RECORD_LOST]);
 	}
 
+	if (session->tool->lost_samples == perf_event__process_lost_samples) {
+		double drop_rate;
+
+		drop_rate = (double)stats->total_lost_samples /
+			    (double) (stats->nr_events[PERF_RECORD_SAMPLE] + stats->total_lost_samples);
+		if (drop_rate > 0.05) {
+			ui__warning("Processed %lu samples and lost %3.2f%% samples!\n\n",
+				    stats->nr_events[PERF_RECORD_SAMPLE] + stats->total_lost_samples,
+				    drop_rate * 100.0);
+		}
+	}
+
 	if (stats->nr_unknown_events != 0) {
 		ui__warning("Found %u unknown events!\n\n"
 			    "Is this an older tool processing a perf.data "