tracing: Add numeric delta time to the trace event benchmark

In order to testing filtering and histograms via the trace event
benchmark, record the delta time of the last event as a numeric value
(currently, it just saves it within the string) so that filters and
histograms can use it.

Link: https://lkml.kernel.org/r/20220906225529.213677569@goodmis.org

Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

kernel/trace/trace_benchmark.c

@@ -51,7 +51,7 @@ static void trace_do_benchmark(void)
 
 	local_irq_disable();
 	start = trace_clock_local();
-	trace_benchmark_event(bm_str);
+	trace_benchmark_event(bm_str, bm_last);
 	stop = trace_clock_local();
 	local_irq_enable();
 

kernel/trace/trace_benchmark.h

@@ -14,19 +14,21 @@ extern void trace_benchmark_unreg(void);
 
 TRACE_EVENT_FN(benchmark_event,
 
-	TP_PROTO(const char *str),
+	TP_PROTO(const char *str, u64 delta),
 
-	TP_ARGS(str),
+	TP_ARGS(str, delta),
 
 	TP_STRUCT__entry(
 		__array(	char,	str,	BENCHMARK_EVENT_STRLEN	)
+		__field(	u64,	delta)
 	),
 
 	TP_fast_assign(
 		memcpy(__entry->str, str, BENCHMARK_EVENT_STRLEN);
+		__entry->delta = delta;
 	),
 
-	TP_printk("%s", __entry->str),
+	TP_printk("%s delta=%llu", __entry->str, __entry->delta),
 
 	trace_benchmark_reg, trace_benchmark_unreg
 );