tracing: Add nohitcount option for suppressing display of raw hitcount

Add 'nohitcount' ('NOHC' for short) option for suppressing display of
the raw hitcount column in the histogram.
Note that you must specify at least one value except raw 'hitcount'
when you specify this nohitcount option.

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

 { pid:          8 }  runtime (%):   3.02  runtime: #
 { pid:         14 }  runtime (%):   2.25  runtime:
 { pid:         16 }  runtime (%):   2.25  runtime:
 { pid:         26 }  runtime (%):   0.17  runtime:
 { pid:         61 }  runtime (%):  11.52  runtime: ####
 { pid:         67 }  runtime (%):   1.56  runtime:
 { pid:         68 }  runtime (%):   0.84  runtime:
 { pid:         76 }  runtime (%):   0.92  runtime:
 { pid:        117 }  runtime (%):   2.50  runtime: #
 { pid:        146 }  runtime (%):  49.88  runtime: ####################
 { pid:        157 }  runtime (%):  16.63  runtime: ######
 { pid:        158 }  runtime (%):   8.38  runtime: ###

Link: https://lore.kernel.org/linux-trace-kernel/166610814787.56030.4980636083486339906.stgit@devnote2

Signed-off-by: Masami Hiramatsu (Google) <[email protected]>
Reviewed-by: Tom Zanussi <[email protected]>
Tested-by: Tom Zanussi <[email protected]>

Author: mhiramat

kernel/trace/trace.c

@@ -5678,6 +5678,7 @@ static const char readme_msg[] =
 	"\t            [:size=#entries]\n"
 	"\t            [:pause][:continue][:clear]\n"
 	"\t            [:name=histname1]\n"
+	"\t            [:nohitcount]\n"
 	"\t            [:<handler>.<action>]\n"
 	"\t            [if <filter>]\n\n"
 	"\t    Note, special fields can be used as well:\n"
@@ -5734,6 +5735,8 @@ static const char readme_msg[] =
 	"\t    The 'clear' parameter will clear the contents of a running\n"
 	"\t    hist trigger and leave its current paused/active state\n"
 	"\t    unchanged.\n\n"
+	"\t    The 'nohitcount' (or NOHC) parameter will suppress display of\n"
+	"\t    raw hitcount in the histogram.\n\n"
 	"\t    The enable_hist and disable_hist triggers can be used to\n"
 	"\t    have one event conditionally start and stop another event's\n"
 	"\t    already-attached hist trigger.  The syntax is analogous to\n"

kernel/trace/trace_events_hist.c

@@ -69,7 +69,8 @@
 	C(INVALID_STR_OPERAND,	"String type can not be an operand in expression"), \
 	C(EXPECT_NUMBER,	"Expecting numeric literal"),		\
 	C(UNARY_MINUS_SUBEXPR,	"Unary minus not supported in sub-expressions"), \
-	C(DIVISION_BY_ZERO,	"Division by zero"),
+	C(DIVISION_BY_ZERO,	"Division by zero"),			\
+	C(NEED_NOHC_VAL,	"Non-hitcount value is required for 'nohitcount'"),
 
 #undef C
 #define C(a, b)		HIST_ERR_##a
@@ -526,6 +527,7 @@ struct hist_trigger_attrs {
 	bool		cont;
 	bool		clear;
 	bool		ts_in_usecs;
+	bool		no_hitcount;
 	unsigned int	map_bits;
 
 	char		*assignment_str[TRACING_MAP_VARS_MAX];
@@ -1550,7 +1552,10 @@ parse_hist_trigger_attrs(struct trace_array *tr, char *trigger_str)
 			ret = parse_assignment(tr, str, attrs);
 			if (ret)
 				goto free;
-		} else if (strcmp(str, "pause") == 0)
+		} else if (strcmp(str, "nohitcount") == 0 ||
+			   strcmp(str, "NOHC") == 0)
+			attrs->no_hitcount = true;
+		else if (strcmp(str, "pause") == 0)
 			attrs->pause = true;
 		else if ((strcmp(str, "cont") == 0) ||
 			 (strcmp(str, "continue") == 0))
@@ -4377,6 +4382,12 @@ static int create_val_fields(struct hist_trigger_data *hist_data,
 	if (fields_str && (strcmp(fields_str, "hitcount") != 0))
 		ret = -EINVAL;
  out:
+	/* There is only raw hitcount but nohitcount suppresses it. */
+	if (j == 1 && hist_data->attrs->no_hitcount) {
+		hist_err(hist_data->event_file->tr, HIST_ERR_NEED_NOHC_VAL, 0);
+		ret = -ENOENT;
+	}
+
 	return ret;
 }
 
@@ -5388,13 +5399,13 @@ static void hist_trigger_entry_print(struct seq_file *m,
 
 	hist_trigger_print_key(m, hist_data, key, elt);
 
-	/* At first, show the raw hitcount always */
-	hist_trigger_print_val(m, i, "hitcount", 0, stats, elt);
+	/* At first, show the raw hitcount if !nohitcount */
+	if (!hist_data->attrs->no_hitcount)
+		hist_trigger_print_val(m, i, "hitcount", 0, stats, 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 (flags & HIST_FIELD_FL_VAR || flags & HIST_FIELD_FL_EXPR)
 			continue;
 
@@ -5839,6 +5850,7 @@ static int event_hist_trigger_print(struct seq_file *m,
 	struct hist_trigger_data *hist_data = data->private_data;
 	struct hist_field *field;
 	bool have_var = false;
+	bool show_val = false;
 	unsigned int i;
 
 	seq_puts(m, HIST_PREFIX);
@@ -5869,12 +5881,16 @@ static int event_hist_trigger_print(struct seq_file *m,
 			continue;
 		}
 
-		if (i == HITCOUNT_IDX)
+		if (i == HITCOUNT_IDX) {
+			if (hist_data->attrs->no_hitcount)
+				continue;
 			seq_puts(m, "hitcount");
-		else {
-			seq_puts(m, ",");
+		} else {
+			if (show_val)
+				seq_puts(m, ",");
 			hist_field_print(m, field);
 		}
+		show_val = true;
 	}
 
 	if (have_var) {
@@ -5925,6 +5941,8 @@ static int event_hist_trigger_print(struct seq_file *m,
 	seq_printf(m, ":size=%u", (1 << hist_data->map->map_bits));
 	if (hist_data->enable_timestamps)
 		seq_printf(m, ":clock=%s", hist_data->attrs->clock);
+	if (hist_data->attrs->no_hitcount)
+		seq_puts(m, ":nohitcount");
 
 	print_actions_spec(m, hist_data);