Commit 45641096 authored by Steven Rostedt's avatar Steven Rostedt Committed by Steven Rostedt (Google)
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tracing: Have hist_debug show what function a field uses 

When CONFIG_HIST_TRIGGERS_DEBUG is enabled, each trace event has a
"hist_debug" file that explains the histogram internal data. This is very
useful for debugging histograms.

One bit of data that was missing from this file was what function a
histogram field uses to process its data. The hist_field structure now has
a fn_num that is used by a switch statement in hist_fn_call() to call a
function directly (to avoid spectre mitigations).

Instead of displaying that number, create a string array that maps to the
histogram function enums so that the function for a field may be
displayed:

 ~# cat /sys/kernel/tracing/events/sched/sched_switch/hist_debug
[..]
hist_data: 0000000043d62762

  n_vals: 2
  n_keys: 1
  n_fields: 3

  val fields:

    hist_data->fields[0]:
      flags:
        VAL: HIST_FIELD_FL_HITCOUNT
      type: u64
      size: 8
      is_signed: 0
      function: hist_field_counter()

    hist_data->fields[1]:
      flags:
        HIST_FIELD_FL_VAR
      var.name: __arg_3921_2
      var.idx (into tracing_map_elt.vars[]): 0
      type: unsigned long[]
      size: 128
      is_signed: 0
      function: hist_field_nop()

  key fields:

    hist_data->fields[2]:
      flags:
        HIST_FIELD_FL_KEY
      ftrace_event_field name: prev_pid
      type: pid_t
      size: 8
      is_signed: 1
      function: hist_field_s32()

The "function:" field above is added.

Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/20260122203822.58df4d80@gandalf.local.home


Reviewed-by: default avatarTom Zanussi <zanussi@kernel.org>
Tested-by: default avatarTom Zanussi <zanussi@kernel.org>
Acked-by: default avatarMasami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 6bdf0730

kernel/trace/trace_events_hist.c

+44 −31
Original line number Diff line number Diff line
@@ -105,38 +105,44 @@ enum field_op_id { 
	FIELD_OP_MULT,

};



#define FIELD_FUNCS					\

	C(NOP,			"nop"),			\

	C(VAR_REF,		"var_ref"),		\

	C(COUNTER,		"counter"),		\

	C(CONST,		"const"),		\

	C(LOG2,			"log2"),		\

	C(BUCKET,		"bucket"),		\

	C(TIMESTAMP,		"timestamp"),		\

	C(CPU,			"cpu"),			\

	C(COMM,			"comm"),		\

	C(STRING,		"string"),		\

	C(DYNSTRING,		"dynstring"),		\

	C(RELDYNSTRING,		"reldynstring"),	\

	C(PSTRING,		"pstring"),		\

	C(S64,			"s64"),			\

	C(U64,			"u64"),			\

	C(S32,			"s32"),			\

	C(U32,			"u32"),			\

	C(S16,			"s16"),			\

	C(U16,			"u16"),			\

	C(S8,			"s8"),			\

	C(U8,			"u8"),			\

	C(UMINUS,		"uminus"),		\

	C(MINUS,		"minus"),		\

	C(PLUS,			"plus"),		\

	C(DIV,			"div"),			\

	C(MULT,			"mult"),		\

	C(DIV_POWER2,		"div_power2"),		\

	C(DIV_NOT_POWER2,	"div_not_power2"),	\

	C(DIV_MULT_SHIFT,	"div_mult_shift"),	\

	C(EXECNAME,		"execname"),		\

	C(STACK,		"stack"),



#undef C

#define C(a, b)		HIST_FIELD_FN_##a



enum hist_field_fn {

	HIST_FIELD_FN_NOP,

	HIST_FIELD_FN_VAR_REF,

	HIST_FIELD_FN_COUNTER,

	HIST_FIELD_FN_CONST,

	HIST_FIELD_FN_LOG2,

	HIST_FIELD_FN_BUCKET,

	HIST_FIELD_FN_TIMESTAMP,

	HIST_FIELD_FN_CPU,

	HIST_FIELD_FN_COMM,

	HIST_FIELD_FN_STRING,

	HIST_FIELD_FN_DYNSTRING,

	HIST_FIELD_FN_RELDYNSTRING,

	HIST_FIELD_FN_PSTRING,

	HIST_FIELD_FN_S64,

	HIST_FIELD_FN_U64,

	HIST_FIELD_FN_S32,

	HIST_FIELD_FN_U32,

	HIST_FIELD_FN_S16,

	HIST_FIELD_FN_U16,

	HIST_FIELD_FN_S8,

	HIST_FIELD_FN_U8,

	HIST_FIELD_FN_UMINUS,

	HIST_FIELD_FN_MINUS,

	HIST_FIELD_FN_PLUS,

	HIST_FIELD_FN_DIV,

	HIST_FIELD_FN_MULT,

	HIST_FIELD_FN_DIV_POWER2,

	HIST_FIELD_FN_DIV_NOT_POWER2,

	HIST_FIELD_FN_DIV_MULT_SHIFT,

	HIST_FIELD_FN_EXECNAME,

	HIST_FIELD_FN_STACK,

	FIELD_FUNCS

};



/*
@@ -5854,6 +5860,12 @@ const struct file_operations event_hist_fops = { 
};



#ifdef CONFIG_HIST_TRIGGERS_DEBUG



#undef C

#define C(a, b)		b



static const char * const field_funcs[] = { FIELD_FUNCS };



static void hist_field_debug_show_flags(struct seq_file *m,

					unsigned long flags)

{
@@ -5918,6 +5930,7 @@ static int hist_field_debug_show(struct seq_file *m, 
	seq_printf(m, "      type: %s\n", field->type);

	seq_printf(m, "      size: %u\n", field->size);

	seq_printf(m, "      is_signed: %u\n", field->is_signed);

	seq_printf(m, "      function: hist_field_%s()\n", field_funcs[field->fn_num]);



	return 0;

}