Commit 54c53dfd authored by Steven Rostedt's avatar Steven Rostedt Committed by Steven Rostedt (Google)
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tracing: Add common_comm to histograms 

If one wants to trace the name of the task that wakes up a process and
pass that to the synthetic events, there's nothing currently that lets the
synthetic events do that. Add a "common_comm" to the histogram logic that
allows histograms save the current->comm as a variable that can be passed
through and added to a synthetic event:

 # cd /sys/kernel/tracing
 # echo 's:wake_lat char[] waker; char[] wakee; u64 delta;' >> dynamic_events
 # echo 'hist:keys=pid:comm=common_comm:ts=common_timestamp.usecs if !(common_flags & 0x18)' > events/sched/sched_waking/trigger
 # echo 'hist:keys=next_pid:wake_comm=$comm:delta=common_timestamp.usecs-$ts:onmatch(sched.sched_waking).trace(wake_lat,$wake_comm,next_comm,$delta)' > events/sched/sched_switch/trigger

The above will create a synthetic trace event that will save both the name
of the waker and the wakee but only if the wakeup did not happen in a hard
or soft interrupt context.

The "common_comm" is used to save the task->comm at the time of the
initial event and is passed via the "comm" variable to the second event,
and that is saved as the "waker" field in the "wake_lat" synthetic event.

Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/20250407154912.3c6c6246@gandalf.local.home


Acked-by: default avatarMasami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: default avatarTom Zanussi <zanussi@kernel.org>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 7ab0fc61

kernel/trace/trace_events_hist.c

+42 −9
Original line number Diff line number Diff line
@@ -114,6 +114,7 @@ enum hist_field_fn { 
	HIST_FIELD_FN_BUCKET,

	HIST_FIELD_FN_TIMESTAMP,

	HIST_FIELD_FN_CPU,

	HIST_FIELD_FN_COMM,

	HIST_FIELD_FN_STRING,

	HIST_FIELD_FN_DYNSTRING,

	HIST_FIELD_FN_RELDYNSTRING,
@@ -506,6 +507,7 @@ enum hist_field_flags { 
	HIST_FIELD_FL_CONST		= 1 << 18,

	HIST_FIELD_FL_PERCENT		= 1 << 19,

	HIST_FIELD_FL_GRAPH		= 1 << 20,

	HIST_FIELD_FL_COMM		= 1 << 21,

};



struct var_defs {
@@ -885,6 +887,15 @@ static u64 hist_field_cpu(struct hist_field *hist_field, 
	return cpu;

}



static u64 hist_field_comm(struct hist_field *hist_field,

			  struct tracing_map_elt *elt,

			  struct trace_buffer *buffer,

			  struct ring_buffer_event *rbe,

			  void *event)

{

	return (u64)(unsigned long)current->comm;

}



/**

 * check_field_for_var_ref - Check if a VAR_REF field references a variable

 * @hist_field: The VAR_REF field to check
@@ -1338,6 +1349,8 @@ static const char *hist_field_name(struct hist_field *field, 
		field_name = hist_field_name(field->operands[0], ++level);

	else if (field->flags & HIST_FIELD_FL_CPU)

		field_name = "common_cpu";

	else if (field->flags & HIST_FIELD_FL_COMM)

		field_name = "common_comm";

	else if (field->flags & HIST_FIELD_FL_EXPR ||

		 field->flags & HIST_FIELD_FL_VAR_REF) {

		if (field->system) {
@@ -2015,6 +2028,13 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data, 
		goto out;

	}



	if (flags & HIST_FIELD_FL_COMM) {

		hist_field->fn_num = HIST_FIELD_FN_COMM;

		hist_field->size = MAX_FILTER_STR_VAL;

		hist_field->type = "char[]";

		goto out;

	}



	if (WARN_ON_ONCE(!field))

		goto out;
@@ -2359,9 +2379,11 @@ parse_field(struct hist_trigger_data *hist_data, struct trace_event_file *file, 
			hist_data->attrs->ts_in_usecs = true;

	} else if (strcmp(field_name, "common_stacktrace") == 0) {

		*flags |= HIST_FIELD_FL_STACKTRACE;

	} else if (strcmp(field_name, "common_cpu") == 0)

	} else if (strcmp(field_name, "common_cpu") == 0) {

		*flags |= HIST_FIELD_FL_CPU;

	else if (strcmp(field_name, "hitcount") == 0)

	} else if (strcmp(field_name, "common_comm") == 0) {

		*flags |= HIST_FIELD_FL_COMM | HIST_FIELD_FL_STRING;

	} else if (strcmp(field_name, "hitcount") == 0)

		*flags |= HIST_FIELD_FL_HITCOUNT;

	else {

		field = trace_find_event_field(file->event_call, field_name);
@@ -2377,6 +2399,8 @@ parse_field(struct hist_trigger_data *hist_data, struct trace_event_file *file, 
				*flags |= HIST_FIELD_FL_CPU;

			} else if (field && field->filter_type == FILTER_STACKTRACE) {

				*flags |= HIST_FIELD_FL_STACKTRACE;

			} else if (field && field->filter_type == FILTER_COMM) {

				*flags |= HIST_FIELD_FL_COMM | HIST_FIELD_FL_STRING;

			} else {

				hist_err(tr, HIST_ERR_FIELD_NOT_FOUND,

					 errpos(field_name));
@@ -4327,6 +4351,8 @@ static u64 hist_fn_call(struct hist_field *hist_field, 
		return hist_field_timestamp(hist_field, elt, buffer, rbe, event);

	case HIST_FIELD_FN_CPU:

		return hist_field_cpu(hist_field, elt, buffer, rbe, event);

	case HIST_FIELD_FN_COMM:

		return hist_field_comm(hist_field, elt, buffer, rbe, event);

	case HIST_FIELD_FN_STRING:

		return hist_field_string(hist_field, elt, buffer, rbe, event);

	case HIST_FIELD_FN_DYNSTRING:
@@ -5212,6 +5238,10 @@ static inline void add_to_key(char *compound_key, void *key, 
	size_t size = key_field->size;



	if (key_field->flags & HIST_FIELD_FL_STRING) {



		if (key_field->flags & HIST_FIELD_FL_COMM) {

			size = strlen((char *)key);

		} else {

			struct ftrace_event_field *field;



			field = key_field->field;
@@ -5220,6 +5250,7 @@ static inline void add_to_key(char *compound_key, void *key, 
				size = *(u32 *)(rec + field->offset) >> 16;

			else if (field->filter_type == FILTER_STATIC_STRING)

				size = field->size;

		}



		/* ensure NULL-termination */

		if (size > key_field->size - 1)
@@ -6097,6 +6128,8 @@ static void hist_field_print(struct seq_file *m, struct hist_field *hist_field) 


	if (hist_field->flags & HIST_FIELD_FL_CPU)

		seq_puts(m, "common_cpu");

	if (hist_field->flags & HIST_FIELD_FL_COMM)

		seq_puts(m, "common_comm");

	else if (hist_field->flags & HIST_FIELD_FL_CONST)

		seq_printf(m, "%llu", hist_field->constant);

	else if (field_name) {