linux-kernel - Re: [PATCH v12 bpf-next 02/12] fprobe: Add ftrace based probe APIs

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Message-ID: <20230608185142.7372e7b6@gandalf.local.home>
Date:   Thu, 8 Jun 2023 18:51:42 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH v12 bpf-next 02/12] fprobe: Add ftrace based probe APIs

On Tue, 15 Mar 2022 23:00:38 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> +static void fprobe_init(struct fprobe *fp)
> +{
> +	fp->nmissed = 0;
> +	fp->ops.func = fprobe_handler;
> +	fp->ops.flags |= FTRACE_OPS_FL_SAVE_REGS;
> +}
> +

Masami,

I thought one of the advantages of fprobes over kprobes was that it did not
need to use SAVE_REGS, as that causes more overhead than SAVE_ARGS?

If fprobes uses save regs, what is the advantage of it over kprobes?

-- Steve