[PATCH 42/46] perf record: Toggle overwrite ring buffer for reading

Wang Nan
2016-02-26T09:36:27Z

Reading from a overwrite ring buffer is unrelible.
perf_evlist__channel_toggle_paused() should be called before
reading from them.

Toggel overwrite_evt_paused director after receiving done or switch
output.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: He Kuang <hekuang@huawei.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
---
tools/perf/builtin-record.c | 79 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 79 insertions(+)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index a069f75..8d247cf 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -40,6 +40,11 @@
#include <sys/mman.h>
#include <asm/bug.h>

+enum overwrite_evt_state {
+ OVERWRITE_EVT_RUNNING,
+ OVERWRITE_EVT_DATA_PENDING,
+ OVERWRITE_EVT_EMPTY,
+};

struct record {
struct perf_tool tool;
@@ -58,6 +63,7 @@ struct record {
bool buildid_all;
bool timestamp_filename;
bool switch_output;
+ enum overwrite_evt_state overwrite_evt_state;
unsigned long long samples;
};

@@ -389,6 +395,7 @@ try_again:

session->evlist = evlist;
perf_session__set_id_hdr_size(session);
+ rec->overwrite_evt_state = OVERWRITE_EVT_RUNNING;
out:
return rc;
}
@@ -469,6 +476,52 @@ static struct perf_event_header finished_round_event = {
.type = PERF_RECORD_FINISHED_ROUND,
};

+static void
+record__toggle_overwrite_evsels(struct record *rec,
+ enum overwrite_evt_state state)
+{
+ struct perf_evlist *evlist = rec->evlist;
+ enum overwrite_evt_state old_state = rec->overwrite_evt_state;
+ enum action {
+ NONE,
+ PAUSE,
+ RESUME,
+ } action = NONE;
+ int ch, nr_channels;
+
+ switch (old_state) {
+ case OVERWRITE_EVT_RUNNING:
+ if (state != OVERWRITE_EVT_RUNNING)
+ action = PAUSE;
+ break;
+ case OVERWRITE_EVT_DATA_PENDING:
+ if (state == OVERWRITE_EVT_RUNNING)
+ action = RESUME;
+ break;
+ case OVERWRITE_EVT_EMPTY:
+ if (state == OVERWRITE_EVT_RUNNING)
+ action = RESUME;
+ if (state == OVERWRITE_EVT_DATA_PENDING)
+ state = OVERWRITE_EVT_EMPTY;
+ break;
+ default:
+ WARN_ONCE(1, "Shouldn't get there\n");
+ }
+
+ rec->overwrite_evt_state = state;
+
+ if (action == NONE)
+ return;
+
+ nr_channels = perf_evlist__channel_nr(evlist);
+ for (ch = 0; ch < nr_channels; ch++) {
+ if (!perf_evlist__channel_check(evlist, ch, RDONLY))
+ continue;
+ perf_evlist__channel_toggle_paused(evlist, ch,
+ action == PAUSE);
+ }
+}
+
static bool record__mmap_should_read(struct record *rec, int idx)
{
int channel = -1;
@@ -513,6 +566,8 @@ static int record__mmap_read_all(struct record *rec)
if (bytes_written != rec->bytes_written)
rc = record__write(rec, &finished_round_event, sizeof(finished_round_event));

+ if (rec->overwrite_evt_state == OVERWRITE_EVT_DATA_PENDING)
+ record__toggle_overwrite_evsels(rec, OVERWRITE_EVT_EMPTY);
out:
return rc;
}
@@ -872,6 +927,17 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
for (;;) {
unsigned long long hits = rec->samples;

+ /*
+ * rec->overwrite_evt_state is possible to be
+ * OVERWRITE_EVT_EMPTY here: when done == true and
+ * hits != rec->samples after previous reading.
+ *
+ * record__toggle_overwrite_evsels ensure we never
+ * convert OVERWRITE_EVT_EMPTY to OVERWRITE_EVT_DATA_PENDING.
+ */
+ if (switch_output_started || done || draining)
+ record__toggle_overwrite_evsels(rec, OVERWRITE_EVT_DATA_PENDING);
+
if (record__mmap_read_all(rec) < 0) {
auxtrace_snapshot_disable();
err = -1;
@@ -890,7 +956,20 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
}

if (switch_output_started) {
+ /*
+ * SIGUSR2 raise after or during record__mmap_read_all().
+ * continue to read again.
+ */
+ if (rec->overwrite_evt_state == OVERWRITE_EVT_RUNNING)
+ continue;
+
switch_output_started = 0;
+ /*
+ * Reenable events in overwrite ring buffer after
+ * record__mmap_read_all(): we should have collected
+ * data from it.
+ */
+ record__toggle_overwrite_evsels(rec, OVERWRITE_EVT_RUNNING);

if (!quiet)
fprintf(stderr, "[ perf record: dump data: Woken up %ld times ]\n",
--
1.8.3.4