linux-kernel - Re: [PATCH v2 24/27] function_graph: Use static_call and branch to optimize entry function

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Date: Mon, 3 Jun 2024 11:07:52 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.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 v2 24/27] function_graph: Use static_call and branch to
 optimize entry function

On Mon, 3 Jun 2024 11:00:18 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> Yes, but that gets a bit complex, and requires the changing of all archs.
> If it starts to become a problem, I rather add that as a feature. That is,
> we can always go back to it. But for now, lets keep the complexity down.

And if we were to go the route of calling a single fgraph_ops caller, I
would want it choreographed with ftrace, such that the direct caller calls
a different fgraph function only if it has only one graph caller on it and
the fgraph loop function if a function has more than one. Just like the
ftrace code does.

If we are going to go that route, let's do it right.

-- Steve