linux-kernel - Re: [PATCH] arm64/ftrace: Make function graph use ftrace directly

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Message-ID: <20220222105218.28e3d5aa@gandalf.local.home>
Date:   Tue, 22 Feb 2022 10:52:18 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Chengming Zhou <zhouchengming@...edance.com>
Cc:     mingo@...hat.com, catalin.marinas@....com, will@...nel.org,
        mark.rutland@....com, broonie@...nel.org, songmuchun@...edance.com,
        qirui.001@...edance.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64/ftrace: Make function graph use ftrace directly

On Tue, 22 Feb 2022 21:00:49 +0800
Chengming Zhou <zhouchengming@...edance.com> wrote:

> As we do in commit 0c0593b45c9b ("x86/ftrace: Make function graph
> use ftrace directly"), we don't need special hook for graph tracer,
> but instead we use graph_ops:func function to install return_hooker.
> 
> Since commit 3b23e4991fb6 ("arm64: implement ftrace with regs") add
> implementation for FTRACE_WITH_REGS on arm64, we can easily adopt
> the same optimization on arm64.

Note. Ideally we want it to hook with DYNAMIC_FTARCE_WITH_ARGS, and not
FTRACE_WITH_REGS. If arm64 is like x86_64, saving all regs at every
function call has a bit more overhead than saving the minimum. The
DYNAMIC_FTRACE_WITH_ARGS, means that the minimum is still saved, but now
exposes the arguments and the stack pointer, which function_graph_tracer
needs.

-- Steve


> 
> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
> ---