ftrace: Show timings of how long nop patching took

Since the beginning of ftrace, the code that did the patching had its
timings saved on how long it took to complete. But this information was
never exposed. It was used for debugging and exposing it was always
something that was on the TODO list. Now it's time to expose it. There's
even a file that is where it should go!

Also include how long patching modules took as a separate value.

 # cat /sys/kernel/tracing/dyn_ftrace_total_info
 57680 pages:231 groups: 9
 ftrace boot update time = 14024666 (ns)
 ftrace module total update time = 126070 (ns)

Cc: Masami Hiramatsu <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: https://lore.kernel.org/[email protected]
Signed-off-by: Steven Rostedt (Google) <[email protected]>

Author: rostedt

kernel/trace/ftrace.c

@@ -3686,7 +3686,8 @@ static int ftrace_hash_move_and_update_subops(struct ftrace_ops *subops,
 }
 
 
-static u64		ftrace_update_time;
+u64			ftrace_update_time;
+u64			ftrace_total_mod_time;
 unsigned long		ftrace_update_tot_cnt;
 unsigned long		ftrace_number_of_pages;
 unsigned long		ftrace_number_of_groups;
@@ -3706,7 +3707,7 @@ static int ftrace_update_code(struct module *mod, struct ftrace_page *new_pgs)
 	bool init_nop = ftrace_need_init_nop();
 	struct ftrace_page *pg;
 	struct dyn_ftrace *p;
-	u64 start, stop;
+	u64 start, stop, update_time;
 	unsigned long update_cnt = 0;
 	unsigned long rec_flags = 0;
 	int i;
@@ -3750,7 +3751,11 @@ static int ftrace_update_code(struct module *mod, struct ftrace_page *new_pgs)
 	}
 
 	stop = ftrace_now(raw_smp_processor_id());
-	ftrace_update_time = stop - start;
+	update_time = stop - start;
+	if (mod)
+		ftrace_total_mod_time += update_time;
+	else
+		ftrace_update_time = update_time;
 	ftrace_update_tot_cnt += update_cnt;
 
 	return 0;

kernel/trace/trace.c

@@ -8548,15 +8548,22 @@ tracing_read_dyn_info(struct file *filp, char __user *ubuf,
 	char *buf;
 	int r;
 
-	/* 256 should be plenty to hold the amount needed */
-	buf = kmalloc(256, GFP_KERNEL);
+	/* 512 should be plenty to hold the amount needed */
+#define DYN_INFO_BUF_SIZE	512
+
+	buf = kmalloc(DYN_INFO_BUF_SIZE, GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;
 
-	r = scnprintf(buf, 256, "%ld pages:%ld groups: %ld\n",
+	r = scnprintf(buf, DYN_INFO_BUF_SIZE,
+		      "%ld pages:%ld groups: %ld\n"
+		      "ftrace boot update time = %llu (ns)\n"
+		      "ftrace module total update time = %llu (ns)\n",
 		      ftrace_update_tot_cnt,
 		      ftrace_number_of_pages,
-		      ftrace_number_of_groups);
+		      ftrace_number_of_groups,
+		      ftrace_update_time,
+		      ftrace_total_mod_time);
 
 	ret = simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
 	kfree(buf);

kernel/trace/trace.h

@@ -775,6 +775,8 @@ extern void trace_event_follow_fork(struct trace_array *tr, bool enable);
 extern unsigned long ftrace_update_tot_cnt;
 extern unsigned long ftrace_number_of_pages;
 extern unsigned long ftrace_number_of_groups;
+extern u64 ftrace_update_time;
+extern u64 ftrace_total_mod_time;
 void ftrace_init_trace_array(struct trace_array *tr);
 #else
 static inline void ftrace_init_trace_array(struct trace_array *tr) { }