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tracing: Have hist_debug show what function a field uses

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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: Tom Zanussi <zanussi@kernel.org>
Tested-by: Tom Zanussi <zanussi@kernel.org>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt 2026-01-22 20:38:22 -05:00 committed by Steven Rostedt (Google)
parent 6bdf07302f
commit 45641096c9
1 changed files with 44 additions and 31 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

75
kernel/trace/trace_events_hist.c
View File

@ -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;
}