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

Steven Rostedt
2024-11-26T00:03:36Z

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

> From: "Mike Rapoport (Microsoft)" <rppt@kernel.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.
>
> Reported-by: Steven Rostedt <rostedt@goodmis.org>

Tested-by: Steven Rostedt (Google) <rostedt@goodmis.org>

-- Steve

> 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@kernel.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