[PATCH v3 12/23] perf: add ITRACE_START record to indicate that tracing has started

Alexander Shishkin
2014-08-11T05:31:58Z

For counters such as instruction tracing, it is useful for the decoder
to know which tasks are running when the event is first scheduled in,
before the first sched_switch.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
---
include/linux/perf_event.h | 3 +++
include/uapi/linux/perf_event.h | 11 +++++++++++
kernel/events/core.c | 41 +++++++++++++++++++++++++++++++++++++++++
3 files changed, 55 insertions(+)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index cb8c92e041..46137cb4d6 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -126,6 +126,9 @@ struct hw_perf_event {
/* for tp_event->class */
struct list_head tp_list;
};
+ struct { /* itrace */
+ int itrace_started;
+ };
#ifdef CONFIG_HAVE_HW_BREAKPOINT
struct { /* breakpoint */
/*
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index b14b1f57c1..500e18b8e9 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -758,6 +758,17 @@ enum perf_event_type {
*/
PERF_RECORD_AUX = 11,

+ /*
+ * Indicates that instruction trace has started
+ *
+ * struct {
+ * struct perf_event_header header;
+ * u32 pid;
+ * u32 tid;
+ * };
+ */
+ PERF_RECORD_ITRACE_START = 12,
+
PERF_RECORD_MAX, /* non-ABI */
};

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 2de7d40cb6..d4b5e33b74 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1671,6 +1671,7 @@ static void perf_set_shadow_time(struct perf_event *event,
#define MAX_INTERRUPTS (~0ULL)

static void perf_log_throttle(struct perf_event *event, int enable);
+static void perf_log_itrace_start(struct perf_event *event);

static int
event_sched_in(struct perf_event *event,
@@ -1705,6 +1706,8 @@ event_sched_in(struct perf_event *event,

perf_pmu_disable(event->pmu);

+ perf_log_itrace_start(event);
+
if (event->pmu->add(event, PERF_EF_START)) {
event->state = PERF_EVENT_STATE_INACTIVE;
event->oncpu = -1;
@@ -5524,6 +5527,44 @@ static void perf_log_throttle(struct perf_event *event, int enable)
perf_output_end(&handle);
}

+static void perf_log_itrace_start(struct perf_event *event)
+{
+ struct perf_output_handle handle;
+ struct perf_sample_data sample;
+ struct perf_aux_event {
+ struct perf_event_header header;
+ u32 pid;
+ u32 tid;
+ } rec;
+ int ret;
+
+ if (event->parent)
+ event = event->parent;
+
+ if (!(event->pmu->capabilities & PERF_PMU_CAP_ITRACE) ||
+ event->hw.itrace_started)
+ return;
+
+ event->hw.itrace_started = 1;
+
+ rec.header.type = PERF_RECORD_ITRACE_START;
+ rec.header.misc = 0;
+ rec.header.size = sizeof(rec);
+ rec.pid = perf_event_pid(event, current);
+ rec.tid = perf_event_tid(event, current);
+
+ perf_event_header__init_id(&rec.header, &sample, event);
+ ret = perf_output_begin(&handle, event, rec.header.size);
+
+ if (ret)
+ return;
+
+ perf_output_put(&handle, rec);
+ perf_event__output_id_sample(event, &handle, &sample);
+
+ perf_output_end(&handle);
+}
+
/*
* Generic event overflow handling, sampling.
*/
--
2.1.0.rc1