linux-kernel - Re: [PATCH v2 0/5] tracepoints: Add warnings for unused tracepoints and trace events

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Message-ID: <20250613104240.509ff13c@batman.local.home>
Date: Fri, 13 Jun 2025 10:42:40 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
 llvm@...ts.linux.dev
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Masami Hiramatsu
 <mhiramat@...nel.org>, Arnd Bergmann <arnd@...db.de>, Masahiro Yamada
 <masahiroy@...nel.org>, Nathan Chancellor <nathan@...nel.org>, Nicolas
 Schier <nicolas.schier@...ux.dev>, Nick Desaulniers
 <nick.desaulniers+lkml@...il.com>, Catalin Marinas
 <catalin.marinas@....com>, Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 0/5] tracepoints: Add warnings for unused tracepoints
 and trace events

On Fri, 13 Jun 2025 10:28:34 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> And each DEFINE_EVENT() is approximately 1296 bytes.
>   ((19559 - 2069) - 5819) / 9

Interesting enough, just raw tracepoints are not much better. I updated
the header file (attached) to have 10 of these, and compiled that.

DECLARE_TRACE(size_event_1,
        TP_PROTO(struct size_event_struct *A, struct size_event_struct *B),
        TP_ARGS(A, B));

The result is:

   text    data     bss     dec     hex filename
    629    1440       0    2069     815 no-events.ko
  44837   15424       0   60261    eb65 trace-events.ko
  11495    8064       0   19559    4c67 define-events.ko
  10865    4408       0   15273    3ba9 declare-trace.ko

Where each DECLARE_TRACE() ends up being 1320 bytes.
  (15273 - 2069) / 10

This is slightly bigger than a DEFINE_EVENT(), but that's also because
the DEFINE_EVENT() shares some of the tracepoint creation in the
DECLARE_EVENT_CLASS(), where as that work is done fully in the
DECLARE_TRACE().

-- Steve

View attachment "size_events.h" of type "text/x-chdr" (7841 bytes)