[PATCH 37/46] perf tools: Detect avalibility of write_backward

Wang Nan
2016-02-26T09:34:22Z

Detect avalibility of write_backward and save the result into
record_opts. With write_backward the start pointer of a ring
buffer mapped read only can be found reliably.

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/perf.h | 1 +
tools/perf/util/record.c | 11 +++++++++++
2 files changed, 12 insertions(+)

diff --git a/tools/perf/perf.h b/tools/perf/perf.h
index 5381a01..198345e 100644
--- a/tools/perf/perf.h
+++ b/tools/perf/perf.h
@@ -73,6 +73,7 @@ struct record_opts {
bool sample_transaction;
unsigned initial_delay;
bool use_clockid;
+ bool has_write_backward;
clockid_t clockid;
unsigned int proc_map_timeout;
};
diff --git a/tools/perf/util/record.c b/tools/perf/util/record.c
index 0467367..d01f155 100644
--- a/tools/perf/util/record.c
+++ b/tools/perf/util/record.c
@@ -85,6 +85,11 @@ static void perf_probe_comm_exec(struct perf_evsel *evsel)
evsel->attr.comm_exec = 1;
}

+static void perf_probe_write_backward(struct perf_evsel *evsel)
+{
+ evsel->attr.write_backward = 1;
+}
+
static void perf_probe_context_switch(struct perf_evsel *evsel)
{
evsel->attr.context_switch = 1;
@@ -105,6 +110,11 @@ bool perf_can_record_switch_events(void)
return perf_probe_api(perf_probe_context_switch);
}

+static bool perf_can_write_backward(void)
+{
+ return perf_probe_api(perf_probe_write_backward);
+}
+
bool perf_can_record_cpu_wide(void)
{
struct perf_event_attr attr = {
@@ -235,6 +245,7 @@ static int record_opts__config_freq(struct record_opts *opts)

int record_opts__config(struct record_opts *opts)
{
+ opts->has_write_backward = perf_can_write_backward();
return record_opts__config_freq(opts);
}

--
1.8.3.4