linux-kernel - [PATCH] init/main.c: print initcall level when initcall

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Message-ID: <20241229162901.126411-1-francesco@valla.it>
Date: Sun, 29 Dec 2024 17:29:01 +0100
From: Francesco Valla <francesco@...la.it>
To: linux-kernel@...r.kernel.org
Cc: linux-embedded@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>,
	Tim Bird <Tim.Bird@...y.com>
Subject: [PATCH] init/main.c: print initcall level when initcall_debug is used

When initcall_debug is specified on the command line, the start and
return point for each initcall is printed. However, no information on
the initcall level is reported.

Add to the initcall_debug infrastructure an additional print that
informs when a new initcall level is entered. This is particularly
useful when debugging dependency chains and/or working on boot time
reduction.

Signed-off-by: Francesco Valla <francesco@...la.it>
---
 init/main.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/init/main.c b/init/main.c
index 00fac1170294..160c93332536 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1223,6 +1223,12 @@ trace_initcall_finish_cb(void *data, initcall_t fn, int ret)
 		 fn, ret, (unsigned long long)ktime_us_delta(rettime, *calltime));
 }
 
+static __init_or_module void
+trace_initcall_level_cb(void *data, const char *level)
+{
+	printk(KERN_DEBUG "entering %s initcall level\n", level);
+}
+
 static ktime_t initcall_calltime;
 
 #ifdef TRACEPOINTS_ENABLED
@@ -1234,10 +1240,12 @@ static void __init initcall_debug_enable(void)
 					    &initcall_calltime);
 	ret |= register_trace_initcall_finish(trace_initcall_finish_cb,
 					      &initcall_calltime);
+	ret |= register_trace_initcall_level(trace_initcall_level_cb, NULL);
 	WARN(ret, "Failed to register initcall tracepoints\n");
 }
 # define do_trace_initcall_start	trace_initcall_start
 # define do_trace_initcall_finish	trace_initcall_finish
+# define do_trace_initcall_level	trace_initcall_level
 #else
 static inline void do_trace_initcall_start(initcall_t fn)
 {
@@ -1251,6 +1259,12 @@ static inline void do_trace_initcall_finish(initcall_t fn, int ret)
 		return;
 	trace_initcall_finish_cb(&initcall_calltime, fn, ret);
 }
+static inline void do_trace_initcall_level(const char *level)
+{
+	if (!initcall_debug)
+		return;
+	trace_initcall_level_cb(NULL, level);
+}
 #endif /* !TRACEPOINTS_ENABLED */
 
 int __init_or_module do_one_initcall(initcall_t fn)
@@ -1323,7 +1337,7 @@ static void __init do_initcall_level(int level, char *command_line)
 		   level, level,
 		   NULL, ignore_unknown_bootoption);
 
-	trace_initcall_level(initcall_level_names[level]);
+	do_trace_initcall_level(initcall_level_names[level]);
 	for (fn = initcall_levels[level]; fn < initcall_levels[level+1]; fn++)
 		do_one_initcall(initcall_from_entry(fn));
 }
@@ -1367,7 +1381,7 @@ static void __init do_pre_smp_initcalls(void)
 {
 	initcall_entry_t *fn;
 
-	trace_initcall_level("early");
+	do_trace_initcall_level("early");
 	for (fn = __initcall_start; fn < __initcall0_start; fn++)
 		do_one_initcall(initcall_from_entry(fn));
 }
-- 
2.47.1