linux-kernel - Re: [PATCH] x86/ftrace: fix boot time slowdown

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Message-Id: <20241125125840.72ff35d6ee542b2c176852af@kernel.org>
Date: Mon, 25 Nov 2024 12:58:40 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Mike Rapoport <rppt@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Borislav Petkov
 <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, Ingo Molnar
 <mingo@...hat.com>, Masami Hiramatsu <mhiramat@...nel.org>, Steven Rostedt
 <rostedt@...dmis.org>, Thomas Gleixner <tglx@...utronix.de>,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 x86@...nel.org
Subject: Re: [PATCH] x86/ftrace: fix boot time slowdown

On Sun, 24 Nov 2024 16:07:05 +0200
Mike Rapoport <rppt@...nel.org> wrote:

> From: "Mike Rapoport (Microsoft)" <rppt@...nel.org>
> 
> Steven Rostedt reported slowdown by over 30ms caused by commit 9bfc4824fd48
> ("x86/module: prepare module loading for ROX allocations of text")
> 
>   Before:
> 
>    # cat /sys/kernel/tracing/dyn_ftrace_total_info
>   57695 pages:231 groups: 9
>   ftrace boot update time = 14733459 (ns)
>   ftrace module total update time = 449016 (ns)
> 
>   After:
> 
>    # cat /sys/kernel/tracing/dyn_ftrace_total_info
>   57708 pages:231 groups: 9
>   ftrace boot update time = 47195374 (ns)
>   ftrace module total update time = 592080 (ns)
> 
> The slowdown happened because initial patching of kernel code for ftrace
> was switched from text_poke_early() to text_poke() to accommodate ftrace
> updates of module text allocated as ROX.
> 
> Restore the use of text_poke_early() for boot time patching of the kernel
> code.
> 

Looks good to me.

Reviewed-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>

Thank you!

> Reported-by: Steven Rostedt <rostedt@...dmis.org>
> Closes: https://lore.kernel.org/all/20241118132501.4eddb46c@gandalf.local.home
> Fixes: 9bfc4824fd48 ("x86/module: prepare module loading for ROX allocations of text")
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
> ---
>  arch/x86/kernel/ftrace.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
> index 4dd0ad6c94d6..9e50288abbaa 100644
> --- a/arch/x86/kernel/ftrace.c
> +++ b/arch/x86/kernel/ftrace.c
> @@ -111,7 +111,7 @@ static int ftrace_verify_code(unsigned long ip, const char *old_code)
>   */
>  static int __ref
>  ftrace_modify_code_direct(unsigned long ip, const char *old_code,
> -			  const char *new_code)
> +			  const char *new_code, struct module *mod)
>  {
>  	int ret = ftrace_verify_code(ip, old_code);
>  	if (ret)
> @@ -120,6 +120,8 @@ ftrace_modify_code_direct(unsigned long ip, const char *old_code,
>  	/* replace the text with the new text */
>  	if (ftrace_poke_late) {
>  		text_poke_queue((void *)ip, new_code, MCOUNT_INSN_SIZE, NULL);
> +	} else if (!mod) {
> +		text_poke_early((void *)ip, new_code, MCOUNT_INSN_SIZE);
>  	} else {
>  		mutex_lock(&text_mutex);
>  		text_poke((void *)ip, new_code, MCOUNT_INSN_SIZE);
> @@ -145,7 +147,7 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long ad
>  	 * just modify the code directly.
>  	 */
>  	if (addr == MCOUNT_ADDR)
> -		return ftrace_modify_code_direct(ip, old, new);
> +		return ftrace_modify_code_direct(ip, old, new, mod);
>  
>  	/*
>  	 * x86 overrides ftrace_replace_code -- this function will never be used
> @@ -164,7 +166,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
>  	new = ftrace_call_replace(ip, addr);
>  
>  	/* Should only be called when module is loaded */
> -	return ftrace_modify_code_direct(rec->ip, old, new);
> +	return ftrace_modify_code_direct(rec->ip, old, new, NULL);
>  }
>  
>  /*
> 
> base-commit: 9f16d5e6f220661f73b36a4be1b21575651d8833
> -- 
> 2.45.2
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>