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tracing: Add support for creating hist trigger variables from literal

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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: Kalesh Singh <kaleshsingh@google.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Kalesh Singh 2021-10-25 13:08:33 -07:00 committed by Steven Rostedt (VMware)
parent 25b9513872
commit 52cfb37353
1 changed files with 70 additions and 1 deletions
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71
kernel/trace/trace_events_hist.c
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@ -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)