From: Tom Zanussi <tom.zanussi@linux.intel.com>
Date: Mon, 26 Jun 2017 17:49:25 -0500
Subject: tracing: Add 'onmax' hist trigger action support
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: c4a6bb1cadf4d24abe6261e58112fa8815300a2c
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

Add an 'onmax(var).save(field,...)' hist trigger action which is
invoked whenever an event exceeds the current maximum.

The end result is that the trace event fields or variables specified
as the onmax.save() params will be saved if 'var' exceeds the current
maximum for that hist trigger entry.  This allows context from the
event that exhibited the new maximum to be saved for later reference.
When the histogram is displayed, additional fields displaying the
saved values will be printed.

As an example the below defines a couple of hist triggers, one for
sched_wakeup and another for sched_switch, keyed on pid.  Whenever a
sched_wakeup occurs, the timestamp is saved in the entry corresponding
to the current pid, and when the scheduler switches back to that pid,
the timestamp difference is calculated.  If the resulting latency
exceeds the current maximum latency, the specified save() values are
saved:

    # echo 'hist:keys=pid:ts0=common_timestamp.usecs \
        if comm=="cyclictest"' >> \
      /sys/kernel/debug/tracing/events/sched/sched_wakeup/trigger

    # echo 'hist:keys=next_pid:\
      wakeup_lat=common_timestamp.usecs-$ts0:\
      onmax($wakeup_lat).save(next_comm,prev_pid,prev_prio,prev_comm) \
        if next_comm=="cyclictest"' >> \
      /sys/kernel/debug/tracing/events/sched/sched_switch/trigger

When the histogram is displayed, the max value and the saved values
corresponding to the max are displayed following the rest of the
fields:

    # cat /sys/kernel/debug/tracing/events/sched/sched_switch/hist
      { next_pid:       2255 } hitcount:        239 \
        common_timestamp-$ts0:          0
        max:         27  next_comm: cyclictest \
        prev_pid:          0  prev_prio:        120  prev_comm: swapper/1 \
      { next_pid:       2256 } hitcount:       2355  common_timestamp-$ts0: 0 \
      	max:         49  next_comm: cyclictest \
        prev_pid:          0  prev_prio:        120  prev_comm: swapper/0

    Totals:
        Hits: 12970
        Entries: 2
        Dropped: 0

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
---
 kernel/trace/trace_events_hist.c |  310 ++++++++++++++++++++++++++++++++++-----
 1 file changed, 276 insertions(+), 34 deletions(-)

--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -282,6 +282,10 @@ struct hist_trigger_data {
 	unsigned int			n_field_var_str;
 	struct field_var_hist		*field_var_hists[SYNTH_FIELDS_MAX];
 	unsigned int			n_field_var_hists;
+
+	struct field_var		*max_vars[SYNTH_FIELDS_MAX];
+	unsigned int			n_max_vars;
+	unsigned int			n_max_var_str;
 };
 
 struct synth_field {
@@ -318,6 +322,12 @@ struct action_data {
 	char			*match_event_system;
 	char			*synth_event_name;
 	struct synth_event	*synth_event;
+
+	char			*onmax_var_str;
+	char			*onmax_fn_name;
+	unsigned int		max_var_ref_idx;
+	struct hist_field	*max_var;
+	struct hist_field	*onmax_var;
 };
 
 static LIST_HEAD(synth_event_list);
@@ -1493,7 +1503,8 @@ static int parse_action(char *str, struc
 	if (attrs->n_actions >= HIST_ACTIONS_MAX)
 		return ret;
 
-	if ((strncmp(str, "onmatch(", strlen("onmatch(")) == 0)) {
+	if ((strncmp(str, "onmatch(", strlen("onmatch(")) == 0) ||
+	    (strncmp(str, "onmax(", strlen("onmax(")) == 0)) {
 		attrs->action_str[attrs->n_actions] = kstrdup(str, GFP_KERNEL);
 		if (!attrs->action_str[attrs->n_actions]) {
 			ret = -ENOMEM;
@@ -1612,7 +1623,7 @@ static void hist_trigger_elt_data_free(s
 	struct hist_elt_data *private_data = elt->private_data;
 	unsigned int i, n_str;
 
-	n_str = hist_data->n_field_var_str;
+	n_str = hist_data->n_field_var_str + hist_data->n_max_var_str;
 
 	for (i = 0; i < n_str; i++)
 		kfree(private_data->field_var_str[i]);
@@ -1647,7 +1658,7 @@ static int hist_trigger_elt_data_alloc(s
 		}
 	}
 
-	n_str = hist_data->n_field_var_str;
+	n_str = hist_data->n_field_var_str + hist_data->n_max_var_str;
 
 	for (i = 0; i < n_str; i++) {
 		elt_data->field_var_str[i] = kzalloc(size, GFP_KERNEL);
@@ -2504,6 +2515,15 @@ static void update_field_vars(struct his
 			    hist_data->n_field_vars, 0);
 }
 
+static void update_max_vars(struct hist_trigger_data *hist_data,
+			    struct tracing_map_elt *elt,
+			    struct ring_buffer_event *rbe,
+			    void *rec)
+{
+	__update_field_vars(elt, rbe, rec, hist_data->max_vars,
+			    hist_data->n_max_vars, hist_data->n_field_var_str);
+}
+
 static struct hist_field *create_var(struct hist_trigger_data *hist_data,
 				     struct trace_event_file *file,
 				     char *name, int size, const char *type)
@@ -2613,6 +2633,222 @@ create_target_field_var(struct hist_trig
 	return create_field_var(hist_data, file, var_name);
 }
 
+static void onmax_print(struct seq_file *m,
+			struct hist_trigger_data *hist_data,
+			struct tracing_map_elt *elt,
+			struct action_data *data)
+{
+	unsigned int i, save_var_idx, max_idx = data->max_var->var.idx;
+
+	seq_printf(m, "\n\tmax: %10llu", tracing_map_read_var(elt, max_idx));
+
+	for (i = 0; i < hist_data->n_max_vars; i++) {
+		struct hist_field *save_val = hist_data->max_vars[i]->val;
+		struct hist_field *save_var = hist_data->max_vars[i]->var;
+		u64 val;
+
+		save_var_idx = save_var->var.idx;
+
+		val = tracing_map_read_var(elt, save_var_idx);
+
+		if (save_val->flags & HIST_FIELD_FL_STRING) {
+			seq_printf(m, "  %s: %-50s", save_var->var.name,
+				   (char *)(uintptr_t)(val));
+		} else
+			seq_printf(m, "  %s: %10llu", save_var->var.name, val);
+	}
+}
+
+static void onmax_save(struct hist_trigger_data *hist_data,
+		       struct tracing_map_elt *elt, void *rec,
+		       struct ring_buffer_event *rbe,
+		       struct action_data *data, u64 *var_ref_vals)
+{
+	unsigned int max_idx = data->max_var->var.idx;
+	unsigned int max_var_ref_idx = data->max_var_ref_idx;
+
+	u64 var_val, max_val;
+
+	var_val = var_ref_vals[max_var_ref_idx];
+	max_val = tracing_map_read_var(elt, max_idx);
+
+	if (var_val <= max_val)
+		return;
+
+	tracing_map_set_var(elt, max_idx, var_val);
+
+	update_max_vars(hist_data, elt, rbe, rec);
+}
+
+static void onmax_destroy(struct action_data *data)
+{
+	unsigned int i;
+
+	destroy_hist_field(data->max_var, 0);
+	destroy_hist_field(data->onmax_var, 0);
+
+	kfree(data->onmax_var_str);
+	kfree(data->onmax_fn_name);
+
+	for (i = 0; i < data->n_params; i++)
+		kfree(data->params[i]);
+
+	kfree(data);
+}
+
+static int onmax_create(struct hist_trigger_data *hist_data,
+			struct action_data *data)
+{
+	struct trace_event_call *call = hist_data->event_file->event_call;
+	struct trace_event_file *file = hist_data->event_file;
+	struct hist_field *var_field, *ref_field, *max_var;
+	unsigned int var_ref_idx = hist_data->n_var_refs;
+	struct field_var *field_var;
+	char *onmax_var_str, *param;
+	const char *event_name;
+	unsigned long flags;
+	unsigned int i;
+	int ret = 0;
+
+	onmax_var_str = data->onmax_var_str;
+	if (onmax_var_str[0] != '$')
+		return -EINVAL;
+	onmax_var_str++;
+
+	event_name = trace_event_name(call);
+	var_field = find_target_event_var(hist_data, NULL, NULL, onmax_var_str);
+	if (!var_field)
+		return -EINVAL;
+
+	flags = HIST_FIELD_FL_VAR_REF;
+	ref_field = create_hist_field(hist_data, NULL, flags, NULL);
+	if (!ref_field)
+		return -ENOMEM;
+
+	ref_field->var.idx = var_field->var.idx;
+	ref_field->var.hist_data = hist_data;
+	ref_field->name = kstrdup(var_field->var.name, GFP_KERNEL);
+	ref_field->type = kstrdup(var_field->type, GFP_KERNEL);
+	if (!ref_field->name || !ref_field->type) {
+		destroy_hist_field(ref_field, 0);
+		ret = -ENOMEM;
+		goto out;
+	}
+	hist_data->var_refs[hist_data->n_var_refs] = ref_field;
+	ref_field->var_ref_idx = hist_data->n_var_refs++;
+	data->onmax_var = ref_field;
+
+	data->fn = onmax_save;
+	data->max_var_ref_idx = var_ref_idx;
+	max_var = create_var(hist_data, file, "max", sizeof(u64), "u64");
+	if (IS_ERR(max_var)) {
+		ret = PTR_ERR(max_var);
+		goto out;
+	}
+	data->max_var = max_var;
+
+	for (i = 0; i < data->n_params; i++) {
+		param = kstrdup(data->params[i], GFP_KERNEL);
+		if (!param)
+			goto out;
+
+		field_var = create_target_field_var(hist_data, NULL, NULL, param);
+		if (IS_ERR(field_var)) {
+			ret = PTR_ERR(field_var);
+			kfree(param);
+			goto out;
+		}
+
+		hist_data->max_vars[hist_data->n_max_vars++] = field_var;
+		if (field_var->val->flags & HIST_FIELD_FL_STRING)
+			hist_data->n_max_var_str++;
+
+		kfree(param);
+	}
+
+	hist_data->actions[hist_data->n_actions++] = data;
+ out:
+	return ret;
+}
+
+static int parse_action_params(char *params, struct action_data *data)
+{
+	char *param, *saved_param;
+	int ret = 0;
+
+	while (params) {
+		if (data->n_params >= SYNTH_FIELDS_MAX)
+			goto out;
+
+		param = strsep(&params, ",");
+		if (!param)
+			goto out;
+
+		param = strstrip(param);
+		if (strlen(param) < 2) {
+			ret = -EINVAL;
+			goto out;
+		}
+
+		saved_param = kstrdup(param, GFP_KERNEL);
+		if (!saved_param) {
+			ret = -ENOMEM;
+			goto out;
+		}
+
+		data->params[data->n_params++] = saved_param;
+	}
+ out:
+	return ret;
+}
+
+static struct action_data *onmax_parse(char *str)
+{
+	char *onmax_fn_name, *onmax_var_str;
+	struct action_data *data;
+	int ret = -EINVAL;
+
+	data = kzalloc(sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return ERR_PTR(-ENOMEM);
+
+	onmax_var_str = strsep(&str, ")");
+	if (!onmax_var_str || !str)
+		return ERR_PTR(-EINVAL);
+	data->onmax_var_str = kstrdup(onmax_var_str, GFP_KERNEL);
+
+	strsep(&str, ".");
+	if (!str)
+		goto free;
+
+	onmax_fn_name = strsep(&str, "(");
+	if (!onmax_fn_name || !str)
+		goto free;
+
+	if (strncmp(onmax_fn_name, "save", strlen("save")) == 0) {
+		char *params = strsep(&str, ")");
+
+		if (!params)
+			goto free;
+
+		ret = parse_action_params(params, data);
+		if (ret)
+			goto free;
+	}
+	data->onmax_fn_name = kstrdup(onmax_fn_name, GFP_KERNEL);
+
+	if (!data->onmax_var_str || !data->onmax_fn_name) {
+		ret = -ENOMEM;
+		goto free;
+	}
+ out:
+	return data;
+ free:
+	onmax_destroy(data);
+	data = ERR_PTR(ret);
+	goto out;
+}
+
 static void onmatch_destroy(struct action_data *data)
 {
 	unsigned int i;
@@ -2689,37 +2925,6 @@ static int check_synth_field(struct synt
 	return 0;
 }
 
-static int parse_action_params(char *params, struct action_data *data)
-{
-	char *param, *saved_param;
-	int ret = 0;
-
-	while (params) {
-		if (data->n_params >= SYNTH_FIELDS_MAX)
-			goto out;
-
-		param = strsep(&params, ",");
-		if (!param)
-			goto out;
-
-		param = strstrip(param);
-		if (strlen(param) < 2) {
-			ret = -EINVAL;
-			goto out;
-		}
-
-		saved_param = kstrdup(param, GFP_KERNEL);
-		if (!saved_param) {
-			ret = -ENOMEM;
-			goto out;
-		}
-
-		data->params[data->n_params++] = saved_param;
-	}
- out:
-	return ret;
-}
-
 static struct hist_field *
 onmatch_find_var(struct hist_trigger_data *hist_data, struct action_data *data,
 		 char *system, char *event, char *var)
@@ -3313,6 +3518,8 @@ static void destroy_actions(struct hist_
 
 		if (data->fn == action_trace)
 			onmatch_destroy(data);
+		else if (data->fn == onmax_save)
+			onmax_destroy(data);
 		else
 			kfree(data);
 	}
@@ -3341,6 +3548,18 @@ static int create_actions(struct hist_tr
 				onmatch_destroy(data);
 				return ret;
 			}
+		} else if (strncmp(str, "onmax(", strlen("onmax(")) == 0) {
+			char *action_str = str + strlen("onmax(");
+
+			data = onmax_parse(action_str);
+			if (IS_ERR(data))
+				return PTR_ERR(data);
+
+			ret = onmax_create(hist_data, data);
+			if (ret) {
+				onmax_destroy(data);
+				return ret;
+			}
 		}
 	}
 
@@ -3355,9 +3574,30 @@ static void print_actions(struct seq_fil
 
 	for (i = 0; i < hist_data->n_actions; i++) {
 		struct action_data *data = hist_data->actions[i];
+
+		if (data->fn == onmax_save)
+			onmax_print(m, hist_data, elt, data);
 	}
 }
 
+static void print_onmax_spec(struct seq_file *m,
+			     struct hist_trigger_data *hist_data,
+			     struct action_data *data)
+{
+	unsigned int i;
+
+	seq_puts(m, ":onmax(");
+	seq_printf(m, "%s", data->onmax_var_str);
+	seq_printf(m, ").%s(", data->onmax_fn_name);
+
+	for (i = 0; i < hist_data->n_max_vars; i++) {
+		seq_printf(m, "%s", hist_data->max_vars[i]->var->var.name);
+		if (i < hist_data->n_max_vars - 1)
+			seq_puts(m, ",");
+	}
+	seq_puts(m, ")");
+}
+
 static void print_onmatch_spec(struct seq_file *m,
 			       struct hist_trigger_data *hist_data,
 			       struct action_data *data)
@@ -3388,6 +3628,8 @@ static void print_actions_spec(struct se
 
 		if (data->fn == action_trace)
 			print_onmatch_spec(m, hist_data, data);
+		else if (data->fn == onmax_save)
+			print_onmax_spec(m, hist_data, data);
 	}
 }