linux-kernel - Re: [PATCH 19/20] function_graph: Use for_each_set_bit() in __ftrace_return_to

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Message-Id: <20240527090434.37e309d0280d6d8f116edc85@kernel.org>
Date: Mon, 27 May 2024 09:04:34 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, Masami
 Hiramatsu <mhiramat@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Andrew Morton
 <akpm@...ux-foundation.org>, Alexei Starovoitov
 <alexei.starovoitov@...il.com>, Florent Revest <revest@...omium.org>,
 Martin KaFai Lau <martin.lau@...ux.dev>, bpf <bpf@...r.kernel.org>, Sven
 Schnelle <svens@...ux.ibm.com>, Alexei Starovoitov <ast@...nel.org>, Jiri
 Olsa <jolsa@...nel.org>, Arnaldo Carvalho de Melo <acme@...nel.org>, Daniel
 Borkmann <daniel@...earbox.net>, Alan Maguire <alan.maguire@...cle.com>,
 Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner
 <tglx@...utronix.de>, Guo Ren <guoren@...nel.org>
Subject: Re: [PATCH 19/20] function_graph: Use for_each_set_bit() in
 __ftrace_return_to_handler()

On Fri, 24 May 2024 22:37:11 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
> 
> Instead of iterating through the entire fgraph_array[] and seeing if one
> of the bitmap bits are set to know to call the array's retfunc() function,
> use for_each_set_bit() on the bitmap itself. This will only iterate for
> the number of set bits.
> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
>  kernel/trace/fgraph.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
> index 4d503b3e45ad..5e8e13ffcfb6 100644
> --- a/kernel/trace/fgraph.c
> +++ b/kernel/trace/fgraph.c
> @@ -827,11 +827,10 @@ static unsigned long __ftrace_return_to_handler(struct fgraph_ret_regs *ret_regs
>  #endif
>  
>  	bitmap = get_bitmap_bits(current, offset);
> -	for (i = 0; i < FGRAPH_ARRAY_SIZE; i++) {
> +
> +	for_each_set_bit(i, &bitmap, sizeof(bitmap) * BITS_PER_BYTE) {
>  		struct fgraph_ops *gops = fgraph_array[i];
>  
> -		if (!(bitmap & BIT(i)))
> -			continue;
>  		if (gops == &fgraph_stub)

Ah, nit: maybe this is unlikely()?

Thank you,


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