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.
Signed-off-by: Kalesh Singh kaleshsingh@google.com Reviewed-by: Namhyung Kim namhyung@kernel.org ---
Changes in v2: - Add description of use case for constants in arithmetic operations, per Steven Rostedt - Add Namhyung's Reviewed-by
kernel/trace/trace_events_hist.c | 80 +++++++++++++++++++++++++++++++- 1 file changed, 79 insertions(+), 1 deletion(-)
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c index f01e442716e2..8563a2d51f65 100644 --- a/kernel/trace/trace_events_hist.c +++ b/kernel/trace/trace_events_hist.c @@ -66,7 +66,9 @@ 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(TOO_MANY_CONSTS, "Too many constants defined"), \ + C(EXPECT_NUMBER, "Expecting numeric literal"),
#undef C #define C(a, b) HIST_ERR_##a @@ -89,6 +91,8 @@ 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_MAX 4 +#define HIST_CONST_DIGITS_MAX 21
enum field_op_id { FIELD_OP_NONE, @@ -152,6 +156,9 @@ 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 +170,15 @@ 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 +357,7 @@ 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 { @@ -410,6 +427,7 @@ struct hist_trigger_data { struct field_var *save_vars[SYNTH_FIELDS_MAX]; unsigned int n_save_vars; unsigned int n_save_var_str; + unsigned int n_constants; };
struct action_data; @@ -1516,6 +1534,12 @@ 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 +1713,15 @@ 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 +2123,35 @@ 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 (hist_data->n_constants >= HIST_CONST_MAX) { + hist_err(tr, HIST_ERR_TOO_MANY_CONSTS, errpos(str)); + return NULL; + } + + 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; + hist_data->n_constants++; + + 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 +2162,15 @@ 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, '.'); @@ -4950,6 +5021,8 @@ 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, @@ -4971,6 +5044,9 @@ 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); @@ -5213,6 +5289,8 @@ 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)