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

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Message-ID:
 <MW5PR13MB563289C2D6F95091501E017AFDAC2@MW5PR13MB5632.namprd13.prod.outlook.com>
Date: Tue, 1 Apr 2025 17:57:22 +0000
From: "Bird, Tim" <Tim.Bird@...y.com>
To: Francesco Valla <francesco@...la.it>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>,
        "linux-embedded@...r.kernel.org"
	<linux-embedded@...r.kernel.org>
CC: Steven Rostedt <rostedt@...dmis.org>,
        Andrew Morton
	<akpm@...ux-foundation.org>
Subject: RE: [PATCH] init/main.c: log initcall level when initcall_debug is
 used

> -----Original Message-----
> From: Francesco Valla <francesco@...la.it>
> 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 2a1757826397..80a07563036d 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -1214,6 +1214,12 @@ 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 initcall level: %s\n", level);
> +}
> +
>  static ktime_t initcall_calltime;
> 
>  #ifdef TRACEPOINTS_ENABLED
> @@ -1225,10 +1231,12 @@ 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)
>  {
> @@ -1242,6 +1250,12 @@ 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)
> @@ -1314,7 +1328,7 @@ 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));
>  }
> @@ -1358,7 +1372,7 @@ 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));
>  }
> --
> 2.48.1

This all looks good to me.  Just to clarify, does tracing have to be enabled to get an
the 'entering initcall level...' printk message?  Or will you get a printk message with
tracing disabled, but initcall_debug specified on the command line?

What do we need to do to push this into mainline?  Based on our discussion in the SIG
meeting, there's no official maintainer for init/main.c.  I recommend pushing this
through Andrew Morton's tree, unless we can think of a better tree to push it through.
Since it does affect a tracer, maybe through Steve's tree?

Another option is for you, Francesco, to become the maintainer of init/main.c (!)
Let me know if you're interested in that.  We'll likely have some more boot-time
things to work on in init/main.c, and it would be nice to have someone managing
this stuff as it comes in.

Thanks, Francesco, for proposing this patch.  I think it will obviate the need for a portion of
my Boot Markers patch, that I suggested at Plumbers last year.
 -- Tim