tracing: Add .percent suffix option to histogram values

Add .percent suffix option to show the histogram values in percentage.
This feature is useful when we need yo undersntand the overall trend
for the histograms of large values.
E.g. this shows the runtime percentage for each tasks.

------
  # cd /sys/kernel/debug/tracing/
  # echo hist:keys=pid:vals=hitcount,runtime.percent:sort=pid > \
    events/sched/sched_stat_runtime/trigger
  # sleep 10
  # cat events/sched/sched_stat_runtime/hist
 # event histogram
 #
 # trigger info: hist:keys=pid:vals=hitcount,runtime.percent:sort=pid:size=2048 [active]
 #

 { pid:          8 } hitcount:          7  runtime (%):   4.14
 { pid:         14 } hitcount:          5  runtime (%):   3.69
 { pid:         16 } hitcount:         11  runtime (%):   3.41
 { pid:         61 } hitcount:         41  runtime (%):  19.75
 { pid:         65 } hitcount:          4  runtime (%):   1.48
 { pid:         70 } hitcount:          6  runtime (%):   3.60
 { pid:         72 } hitcount:          2  runtime (%):   1.10
 { pid:        144 } hitcount:         10  runtime (%):  32.01
 { pid:        151 } hitcount:          8  runtime (%):  22.66
 { pid:        152 } hitcount:          2  runtime (%):   8.10

 Totals:
     Hits: 96
     Entries: 10
     Dropped: 0
-----

Link: https://lore.kernel.org/linux-trace-kernel/166610813077.56030.4238090506973562347.stgit@devnote2Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Tom Zanussi <zanussi@kernel.org>
Tested-by: Tom Zanussi <zanussi@kernel.org>

kernel/trace/trace.c

@@ -5724,7 +5724,8 @@ static const char readme_msg[] =
 	"\t            .syscall    display a syscall id as a syscall name\n"
 	"\t            .log2       display log2 value rather than raw number\n"
 	"\t            .buckets=size  display values in groups of size rather than raw number\n"
-	"\t            .usecs      display a common_timestamp in microseconds\n\n"
+	"\t            .usecs      display a common_timestamp in microseconds\n"
+	"\t            .percent    display a number of percentage value\n\n"
 	"\t    The 'pause' parameter can be used to pause an existing hist\n"
 	"\t    trigger or to start a hist trigger but not log any events\n"
 	"\t    until told to do so.  'continue' can be used to start or\n"

kernel/trace/trace_events_hist.c

@@ -506,6 +506,7 @@ enum hist_field_flags {
 	HIST_FIELD_FL_ALIAS		= 1 << 16,
 	HIST_FIELD_FL_BUCKET		= 1 << 17,
 	HIST_FIELD_FL_CONST		= 1 << 18,
+	HIST_FIELD_FL_PERCENT		= 1 << 19,
 };
 
 struct var_defs {
@@ -1707,6 +1708,8 @@ static const char *get_hist_field_flags(struct hist_field *hist_field)
 		flags_str = "buckets";
 	else if (hist_field->flags & HIST_FIELD_FL_TIMESTAMP_USECS)
 		flags_str = "usecs";
+	else if (hist_field->flags & HIST_FIELD_FL_PERCENT)
+		flags_str = "percent";
 
 	return flags_str;
 }
@@ -2315,6 +2318,10 @@ parse_field(struct hist_trigger_data *hist_data, struct trace_event_file *file,
 			if (ret || !(*buckets))
 				goto error;
 			*flags |= HIST_FIELD_FL_BUCKET;
+		} else if (strncmp(modifier, "percent", 7) == 0) {
+			if (*flags & (HIST_FIELD_FL_VAR | HIST_FIELD_FL_KEY))
+				goto error;
+			*flags |= HIST_FIELD_FL_PERCENT;
 		} else {
  error:
 			hist_err(tr, HIST_ERR_BAD_FIELD_MODIFIER, errpos(modifier));
@@ -5291,33 +5298,69 @@ static void hist_trigger_print_key(struct seq_file *m,
 	seq_puts(m, "}");
 }
 
+/* Get the 100 times of the percentage of @val in @total */
+static inline unsigned int __get_percentage(u64 val, u64 total)
+{
+	if (!total)
+		goto div0;
+
+	if (val < (U64_MAX / 10000))
+		return (unsigned int)div64_ul(val * 10000, total);
+
+	total = div64_u64(total, 10000);
+	if (!total)
+		goto div0;
+
+	return (unsigned int)div64_ul(val, total);
+div0:
+	return val ? UINT_MAX : 0;
+}
+
+static void hist_trigger_print_val(struct seq_file *m, unsigned int idx,
+				   const char *field_name, unsigned long flags,
+				   u64 *totals, struct tracing_map_elt *elt)
+{
+	u64 val = tracing_map_read_sum(elt, idx);
+	unsigned int pc;
+
+	if (flags & HIST_FIELD_FL_PERCENT) {
+		pc = __get_percentage(val, totals[idx]);
+		if (pc == UINT_MAX)
+			seq_printf(m, " %s (%%):[ERROR]", field_name);
+		else
+			seq_printf(m, " %s (%%): %3u.%02u", field_name,
+					pc / 100, pc % 100);
+	} else if (flags & HIST_FIELD_FL_HEX) {
+		seq_printf(m, " %s: %10llx", field_name, val);
+	} else {
+		seq_printf(m, " %s: %10llu", field_name, val);
+	}
+}
+
 static void hist_trigger_entry_print(struct seq_file *m,
 				     struct hist_trigger_data *hist_data,
+				     u64 *totals,
 				     void *key,
 				     struct tracing_map_elt *elt)
 {
 	const char *field_name;
-	unsigned int i;
+	unsigned int i = HITCOUNT_IDX;
+	unsigned long flags;
 
 	hist_trigger_print_key(m, hist_data, key, elt);
 
-	seq_printf(m, " hitcount: %10llu",
-		   tracing_map_read_sum(elt, HITCOUNT_IDX));
+	/* At first, show the raw hitcount always */
+	hist_trigger_print_val(m, i, "hitcount", 0, totals, elt);
 
 	for (i = 1; i < hist_data->n_vals; i++) {
 		field_name = hist_field_name(hist_data->fields[i], 0);
+		flags = hist_data->fields[i]->flags;
 
-		if (hist_data->fields[i]->flags & HIST_FIELD_FL_VAR ||
-		    hist_data->fields[i]->flags & HIST_FIELD_FL_EXPR)
+		if (flags & HIST_FIELD_FL_VAR || flags & HIST_FIELD_FL_EXPR)
 			continue;
 
-		if (hist_data->fields[i]->flags & HIST_FIELD_FL_HEX) {
-			seq_printf(m, "  %s: %10llx", field_name,
-				   tracing_map_read_sum(elt, i));
-		} else {
-			seq_printf(m, "  %s: %10llu", field_name,
-				   tracing_map_read_sum(elt, i));
-		}
+		seq_puts(m, " ");
+		hist_trigger_print_val(m, i, field_name, flags, totals, elt);
 	}
 
 	print_actions(m, hist_data, elt);
@@ -5330,7 +5373,8 @@ static int print_entries(struct seq_file *m,
 {
 	struct tracing_map_sort_entry **sort_entries = NULL;
 	struct tracing_map *map = hist_data->map;
-	int i, n_entries;
+	int i, j, n_entries;
+	u64 *totals = NULL;
 
 	n_entries = tracing_map_sort_entries(map, hist_data->sort_keys,
 					     hist_data->n_sort_keys,
@@ -5338,11 +5382,29 @@ static int print_entries(struct seq_file *m,
 	if (n_entries < 0)
 		return n_entries;
 
+	for (j = 0; j < hist_data->n_vals; j++) {
+		if (!(hist_data->fields[j]->flags & HIST_FIELD_FL_PERCENT))
+			continue;
+		if (!totals) {
+			totals = kcalloc(hist_data->n_vals, sizeof(u64),
+					 GFP_KERNEL);
+			if (!totals) {
+				n_entries = -ENOMEM;
+				goto out;
+			}
+		}
+		for (i = 0; i < n_entries; i++)
+			totals[j] += tracing_map_read_sum(
+					sort_entries[i]->elt, j);
+	}
+
 	for (i = 0; i < n_entries; i++)
-		hist_trigger_entry_print(m, hist_data,
+		hist_trigger_entry_print(m, hist_data, totals,
 					 sort_entries[i]->key,
 					 sort_entries[i]->elt);
 
+	kfree(totals);
+out:
 	tracing_map_destroy_sort_entries(sort_entries, n_entries);
 
 	return n_entries;