Commit 52cfb373 authored by Kalesh Singh's avatar Kalesh Singh Committed by Steven Rostedt (VMware)
Browse files

tracing: Add support for creating hist trigger variables from literal 

Currently hist trigger expressions don't support the use of numeric
literals:
	e.g. echo 'hist:keys=common_pid:x=$y-1234'
		--> is not valid expression syntax

Having the ability to use numeric constants in hist triggers supports
a wider range of expressions for creating variables.

Add support for creating trace event histogram variables from numeric
literals.

	e.g. echo 'hist:keys=common_pid:x=1234,y=size-1024' >> event/trigger

A negative numeric constant is created, using unary minus operator
(parentheses are required).

	e.g. echo 'hist:keys=common_pid:z=-(2)' >> event/trigger

Constants can be used with division/multiplication (added in the
next patch in this series) to implement granularity filters for frequent
trace events. For instance we can limit emitting the rss_stat
trace event to when there is a 512KB cross over in the rss size:

  # Create a synthetic event to monitor instead of the high frequency
  # rss_stat event
  echo 'rss_stat_throttled unsigned int mm_id; unsigned int curr;
	int member; long size' >> tracing/synthetic_events

  # Create a hist trigger that emits the synthetic rss_stat_throttled
  # event only when the rss size crosses a 512KB boundary.
  echo 'hist:keys=keys=mm_id,member:bucket=size/0x80000:onchange($bucket)
      .rss_stat_throttled(mm_id,curr,member,size)'
        >> events/kmem/rss_stat/trigger

A use case for using constants with addition/subtraction is not yet
known, but for completeness the use of constants are supported for all
operators.

Link: https://lkml.kernel.org/r/20211025200852.3002369-2-kaleshsingh@google.com



Signed-off-by: default avatarKalesh Singh <kaleshsingh@google.com>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 25b95138

kernel/trace/trace_events_hist.c

+70 −1
Original line number Diff line number Diff line
@@ -66,7 +66,8 @@ 
	C(EMPTY_SORT_FIELD,	"Empty sort field"),			\

	C(TOO_MANY_SORT_FIELDS,	"Too many sort fields (Max = 2)"),	\

	C(INVALID_SORT_FIELD,	"Sort field must be a key or a val"),	\

	C(INVALID_STR_OPERAND,	"String type can not be an operand in expression"),

	C(INVALID_STR_OPERAND,	"String type can not be an operand in expression"), \

	C(EXPECT_NUMBER,	"Expecting numeric literal"),



#undef C

#define C(a, b)		HIST_ERR_##a
@@ -89,6 +90,7 @@ typedef u64 (*hist_field_fn_t) (struct hist_field *field, 
#define HIST_FIELD_OPERANDS_MAX	2

#define HIST_FIELDS_MAX		(TRACING_MAP_FIELDS_MAX + TRACING_MAP_VARS_MAX)

#define HIST_ACTIONS_MAX	8

#define HIST_CONST_DIGITS_MAX	21



enum field_op_id {

	FIELD_OP_NONE,
@@ -152,6 +154,9 @@ struct hist_field { 
	bool                            read_once;



	unsigned int			var_str_idx;



	/* Numeric literals are represented as u64 */

	u64				constant;

};



static u64 hist_field_none(struct hist_field *field,
@@ -163,6 +168,15 @@ static u64 hist_field_none(struct hist_field *field, 
	return 0;

}



static u64 hist_field_const(struct hist_field *field,

			   struct tracing_map_elt *elt,

			   struct trace_buffer *buffer,

			   struct ring_buffer_event *rbe,

			   void *event)

{

	return field->constant;

}



static u64 hist_field_counter(struct hist_field *field,

			      struct tracing_map_elt *elt,

			      struct trace_buffer *buffer,
@@ -341,6 +355,7 @@ enum hist_field_flags { 
	HIST_FIELD_FL_CPU		= 1 << 15,

	HIST_FIELD_FL_ALIAS		= 1 << 16,

	HIST_FIELD_FL_BUCKET		= 1 << 17,

	HIST_FIELD_FL_CONST		= 1 << 18,

};



struct var_defs {
@@ -1516,6 +1531,12 @@ static void expr_field_str(struct hist_field *field, char *expr) 
{

	if (field->flags & HIST_FIELD_FL_VAR_REF)

		strcat(expr, "$");

	else if (field->flags & HIST_FIELD_FL_CONST) {

		char str[HIST_CONST_DIGITS_MAX];



		snprintf(str, HIST_CONST_DIGITS_MAX, "%llu", field->constant);

		strcat(expr, str);

	}



	strcat(expr, hist_field_name(field, 0));
@@ -1689,6 +1710,15 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data, 
		goto out;

	}



	if (flags & HIST_FIELD_FL_CONST) {

		hist_field->fn = hist_field_const;

		hist_field->size = sizeof(u64);

		hist_field->type = kstrdup("u64", GFP_KERNEL);

		if (!hist_field->type)

			goto free;

		goto out;

	}



	if (flags & HIST_FIELD_FL_STACKTRACE) {

		hist_field->fn = hist_field_none;

		goto out;
@@ -2090,6 +2120,29 @@ static struct hist_field *create_alias(struct hist_trigger_data *hist_data, 
	return alias;

}



static struct hist_field *parse_const(struct hist_trigger_data *hist_data,

				      char *str, char *var_name,

				      unsigned long *flags)

{

	struct trace_array *tr = hist_data->event_file->tr;

	struct hist_field *field = NULL;

	u64 constant;



	if (kstrtoull(str, 0, &constant)) {

		hist_err(tr, HIST_ERR_EXPECT_NUMBER, errpos(str));

		return NULL;

	}



	*flags |= HIST_FIELD_FL_CONST;

	field = create_hist_field(hist_data, NULL, *flags, var_name);

	if (!field)

		return NULL;



	field->constant = constant;



	return field;

}



static struct hist_field *parse_atom(struct hist_trigger_data *hist_data,

				     struct trace_event_file *file, char *str,

				     unsigned long *flags, char *var_name)
@@ -2100,6 +2153,15 @@ static struct hist_field *parse_atom(struct hist_trigger_data *hist_data, 
	unsigned long buckets = 0;

	int ret = 0;



	if (isdigit(str[0])) {

		hist_field = parse_const(hist_data, str, var_name, flags);

		if (!hist_field) {

			ret = -EINVAL;

			goto out;

		}

		return hist_field;

	}



	s = strchr(str, '.');

	if (s) {

		s = strchr(++s, '.');
@@ -4945,6 +5007,8 @@ static void hist_field_debug_show_flags(struct seq_file *m, 


	if (flags & HIST_FIELD_FL_ALIAS)

		seq_puts(m, "        HIST_FIELD_FL_ALIAS\n");

	else if (flags & HIST_FIELD_FL_CONST)

		seq_puts(m, "        HIST_FIELD_FL_CONST\n");

}



static int hist_field_debug_show(struct seq_file *m,
@@ -4966,6 +5030,9 @@ static int hist_field_debug_show(struct seq_file *m, 
			   field->var.idx);

	}



	if (field->flags & HIST_FIELD_FL_CONST)

		seq_printf(m, "      constant: %llu\n", field->constant);



	if (field->flags & HIST_FIELD_FL_ALIAS)

		seq_printf(m, "      var_ref_idx (into hist_data->var_refs[]): %u\n",

			   field->var_ref_idx);
@@ -5208,6 +5275,8 @@ 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");

	else if (hist_field->flags & HIST_FIELD_FL_CONST)

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

	else if (field_name) {

		if (hist_field->flags & HIST_FIELD_FL_VAR_REF ||

		    hist_field->flags & HIST_FIELD_FL_ALIAS)