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Subject[tip:perf/core] perf record: Read from overwritable ring buffer
Commit-ID:  057374645bd42e8bcf22aa4529f99cf7c920a1c6
Gitweb: http://git.kernel.org/tip/057374645bd42e8bcf22aa4529f99cf7c920a1c6
Author: Wang Nan <wangnan0@huawei.com>
AuthorDate: Thu, 14 Jul 2016 08:34:43 +0000
Committer: Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Fri, 15 Jul 2016 17:27:50 -0300

perf record: Read from overwritable ring buffer

Drive the evlist->bkw_mmap_state state machine during draining and when
SIGUSR2 is received. Read the backward ring buffer in record__mmap_read_all.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Nilay Vaish <nilayvaish@gmail.com>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1468485287-33422-12-git-send-email-wangnan0@huawei.com
Signed-off-by: He Kuang <hekuang@huawei.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/builtin-record.c | 31 ++++++++++++++++++++++++++++++-
1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index d4f15e7..b87070b 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -555,7 +555,7 @@ static int record__mmap_read_all(struct record *rec)
if (err)
return err;

- return err;
+ return record__mmap_read_evlist(rec, rec->evlist, true);
}

static void record__init_features(struct record *rec)
@@ -953,6 +953,17 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
for (;;) {
unsigned long long hits = rec->samples;

+ /*
+ * rec->evlist->bkw_mmap_state is possible to be
+ * BKW_MMAP_EMPTY here: when done == true and
+ * hits != rec->samples in previous round.
+ *
+ * perf_evlist__toggle_bkw_mmap ensure we never
+ * convert BKW_MMAP_EMPTY to BKW_MMAP_DATA_PENDING.
+ */
+ if (trigger_is_hit(&switch_output_trigger) || done || draining)
+ perf_evlist__toggle_bkw_mmap(rec->evlist, BKW_MMAP_DATA_PENDING);
+
if (record__mmap_read_all(rec) < 0) {
trigger_error(&auxtrace_snapshot_trigger);
trigger_error(&switch_output_trigger);
@@ -972,8 +983,26 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
}

if (trigger_is_hit(&switch_output_trigger)) {
+ /*
+ * If switch_output_trigger is hit, the data in
+ * overwritable ring buffer should have been collected,
+ * so bkw_mmap_state should be set to BKW_MMAP_EMPTY.
+ *
+ * If SIGUSR2 raise after or during record__mmap_read_all(),
+ * record__mmap_read_all() didn't collect data from
+ * overwritable ring buffer. Read again.
+ */
+ if (rec->evlist->bkw_mmap_state == BKW_MMAP_RUNNING)
+ continue;
trigger_ready(&switch_output_trigger);

+ /*
+ * Reenable events in overwrite ring buffer after
+ * record__mmap_read_all(): we should have collected
+ * data from it.
+ */
+ perf_evlist__toggle_bkw_mmap(rec->evlist, BKW_MMAP_RUNNING);
+
if (!quiet)
fprintf(stderr, "[ perf record: dump data: Woken up %ld times ]\n",
waking);
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