[PATCH v2 14/40] tracing: Add hist trigger timestamp support

[Tom Zanussi]

Add support for a timestamp event field.  This is actually a 'pseudo-'
event field in that it behaves like it's part of the event record, but
is really part of the corresponding ring buffer event.

To make use of the timestamp field, users can specify
"$common_timestamp" as a field name for any histogram.  Note that this
doesn't make much sense on its own either as either a key or value,
but needs to be supported even so, since follow-on patches will add
support for making use of this field in time deltas.  The '$' is used
as a prefix on the variable name to indicate that it's not an bonafide
event field - so you won't find it in the event description - but
rather it's a synthetic field that can be used like a real field).

Note that the use of this field requires the ring buffer be put into
TIME_EXTEND_ABS mode, which saves the complete timestamp for each
event rather than an offset.  This mode will be enabled if and only if
a histogram makes use of the "$common_timestamp" field.

Signed-off-by: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
---
 kernel/trace/trace_events_hist.c | 88 +++++++++++++++++++++++++++++-----------
 1 file changed, 65 insertions(+), 23 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 3d92faa..dfaf07b 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -89,6 +89,12 @@ static u64 hist_field_log2(struct hist_field *hist_field, void *event,
 	return (u64) ilog2(roundup_pow_of_two(val));
 }
 
+static u64 hist_field_timestamp(struct hist_field *hist_field, void *event,
+				struct ring_buffer_event *rbe)
+{
+	return ring_buffer_event_time_stamp(rbe);
+}
+
 #define DEFINE_HIST_FIELD_FN(type)					\
 	static u64 hist_field_##type(struct hist_field *hist_field,	\
 				     void *event,			\
@@ -135,6 +141,7 @@ enum hist_field_flags {
 	HIST_FIELD_FL_SYSCALL		= 128,
 	HIST_FIELD_FL_STACKTRACE	= 256,
 	HIST_FIELD_FL_LOG2		= 512,
+	HIST_FIELD_FL_TIMESTAMP		= 1024,
 };
 
 struct hist_trigger_attrs {
@@ -159,6 +166,7 @@ struct hist_trigger_data {
 	struct trace_event_file		*event_file;
 	struct hist_trigger_attrs	*attrs;
 	struct tracing_map		*map;
+	bool				enable_timestamps;
 };
 
 static const char *hist_field_name(struct hist_field *field,
@@ -173,6 +181,8 @@ static const char *hist_field_name(struct hist_field *field,
 		field_name = field->field->name;
 	else if (field->flags & HIST_FIELD_FL_LOG2)
 		field_name = hist_field_name(field->operands[0], ++level);
+	else if (field->flags & HIST_FIELD_FL_TIMESTAMP)
+		field_name = "$common_timestamp";
 
 	if (field_name == NULL)
 		field_name = "";
@@ -424,6 +434,12 @@ static struct hist_field *create_hist_field(struct ftrace_event_field *field,
 		goto out;
 	}
 
+	if (flags & HIST_FIELD_FL_TIMESTAMP) {
+		hist_field->fn = hist_field_timestamp;
+		hist_field->size = sizeof(u64);
+		goto out;
+	}
+
 	if (WARN_ON_ONCE(!field))
 		goto out;
 
@@ -501,10 +517,15 @@ static int create_val_field(struct hist_trigger_data *hist_data,
 		}
 	}
 
-	field = trace_find_event_field(file->event_call, field_name);
-	if (!field || !field->size) {
-		ret = -EINVAL;
-		goto out;
+	if (strcmp(field_name, "$common_timestamp") == 0) {
+		flags |= HIST_FIELD_FL_TIMESTAMP;
+		hist_data->enable_timestamps = true;
+	} else {
+		field = trace_find_event_field(file->event_call, field_name);
+		if (!field || !field->size) {
+			ret = -EINVAL;
+			goto out;
+		}
 	}
 
 	hist_data->fields[val_idx] = create_hist_field(field, flags);
@@ -599,16 +620,22 @@ static int create_key_field(struct hist_trigger_data *hist_data,
 			}
 		}
 
-		field = trace_find_event_field(file->event_call, field_name);
-		if (!field || !field->size) {
-			ret = -EINVAL;
-			goto out;
-		}
+		if (strcmp(field_name, "$common_timestamp") == 0) {
+			flags |= HIST_FIELD_FL_TIMESTAMP;
+			hist_data->enable_timestamps = true;
+			key_size = sizeof(u64);
+		} else {
+			field = trace_find_event_field(file->event_call, field_name);
+			if (!field || !field->size) {
+				ret = -EINVAL;
+				goto out;
+			}
 
-		if (is_string_field(field))
-			key_size = MAX_FILTER_STR_VAL;
-		else
-			key_size = field->size;
+			if (is_string_field(field))
+				key_size = MAX_FILTER_STR_VAL;
+			else
+				key_size = field->size;
+		}
 	}
 
 	hist_data->fields[key_idx] = create_hist_field(field, flags);
@@ -804,6 +831,9 @@ static int create_tracing_map_fields(struct hist_trigger_data *hist_data)
 
 			if (hist_field->flags & HIST_FIELD_FL_STACKTRACE)
 				cmp_fn = tracing_map_cmp_none;
+			else if (!field)
+				cmp_fn = tracing_map_cmp_num(hist_field->size,
+							     hist_field->is_signed);
 			else if (is_string_field(field))
 				cmp_fn = tracing_map_cmp_string;
 			else
@@ -1201,7 +1231,11 @@ static void hist_field_print(struct seq_file *m, struct hist_field *hist_field)
 {
 	const char *field_name = hist_field_name(hist_field, 0);
 
-	seq_printf(m, "%s", field_name);
+	if (hist_field->flags & HIST_FIELD_FL_TIMESTAMP)
+		seq_puts(m, "$common_timestamp");
+	else if (field_name)
+		seq_printf(m, "%s", field_name);
+
 	if (hist_field->flags) {
 		const char *flags_str = get_hist_field_flags(hist_field);
 
@@ -1252,27 +1286,25 @@ static int event_hist_trigger_print(struct seq_file *m,
 
 	for (i = 0; i < hist_data->n_sort_keys; i++) {
 		struct tracing_map_sort_key *sort_key;
+		unsigned int idx;
 
 		sort_key = &hist_data->sort_keys[i];
+		idx = sort_key->field_idx;
+
+		if (WARN_ON(idx >= TRACING_MAP_FIELDS_MAX))
+			return -EINVAL;
 
 		if (i > 0)
 			seq_puts(m, ",");
 
-		if (sort_key->field_idx == HITCOUNT_IDX)
+		if (idx == HITCOUNT_IDX)
 			seq_puts(m, "hitcount");
-		else {
-			unsigned int idx = sort_key->field_idx;
-
-			if (WARN_ON(idx >= TRACING_MAP_FIELDS_MAX))
-				return -EINVAL;
-
+		else
 			hist_field_print(m, hist_data->fields[idx]);
-		}
 
 		if (sort_key->descending)
 			seq_puts(m, ".descending");
 	}
-
 	seq_printf(m, ":size=%u", (1 << hist_data->map->map_bits));
 
 	if (data->filter_str)
@@ -1440,6 +1472,10 @@ static bool hist_trigger_match(struct event_trigger_data *data,
 			return false;
 		if (key_field->offset != key_field_test->offset)
 			return false;
+		if (key_field->size != key_field_test->size)
+			return false;
+		if (key_field->is_signed != key_field_test->is_signed)
+			return false;
 	}
 
 	for (i = 0; i < hist_data->n_sort_keys; i++) {
@@ -1522,6 +1558,9 @@ static int hist_register_trigger(char *glob, struct event_trigger_ops *ops,
 
 	update_cond_flag(file);
 
+	if (hist_data->enable_timestamps)
+		tracing_set_time_stamp_abs(file->tr, true);
+
 	if (trace_event_trigger_enable_disable(file, 1) < 0) {
 		list_del_rcu(&data->list);
 		update_cond_flag(file);
@@ -1556,6 +1595,9 @@ static void hist_unregister_trigger(char *glob, struct event_trigger_ops *ops,
 
 	if (unregistered && test->ops->free)
 		test->ops->free(test->ops, test);
+
+	if (hist_data->enable_timestamps)
+		tracing_set_time_stamp_abs(file->tr, false);
 }
 
 static void hist_unreg_all(struct trace_event_file *file)
-- 
1.9.3