linux-kernel - Re: [RFC PATCH -next v2 3/4] arm64/ftrace: support dynamically allocated trampolines

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Date:   Thu, 21 Apr 2022 10:08:59 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Wang ShaoBo <bobo.shaobowang@...wei.com>, cj.chengjian@...wei.com,
        huawei.libin@...wei.com, xiexiuqi@...wei.com, liwei391@...wei.com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        catalin.marinas@....com, will@...nel.org, zengshun.wu@...look.com
Subject: Re: [RFC PATCH -next v2 3/4] arm64/ftrace: support dynamically
 allocated trampolines

On Thu, 21 Apr 2022 10:06:39 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> Without this change, because the arch does not support dynamically
> allocated trampolines, it means that all these ftrace_ops will be
> registered to the same trampoline. That means, for every function that is
> traced, it will loop through all 10 of theses ftrace_ops and check their
> hashes to see if their callback should be called or not.

Oh, I forgot to mention. If you then enable function tracer that traces
*every function*, then *every function* will be going through this loop of
the 10 ftrace_ops!

With dynamically allocated trampolines, then most functions will just call
the trampoline that handles the function tracer directly.

-- Steve