linux-kernel - Re: [PATCH 1/3 v2] tracepoints: Add helper to test if tracepoint is enabled in a header

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Date:   Tue, 20 Oct 2020 13:59:46 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org
Cc:     Yafang Shao <laoar.shao@...il.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michel Lespinasse <walken@...gle.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        Davidlohr Bueso <dbueso@...e.de>,
        Linux MM <linux-mm@...ck.org>, Ingo Molnar <mingo@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH 1/3 v2] tracepoints: Add helper to test if tracepoint is
 enabled in a header

On 9/25/20 11:12 PM, Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> 
> As tracepoints are discouraged from being added in a header because it can
> cause side effects if other tracepoints are in headers, as well as bloat the
> kernel as the trace_<tracepoint>() function is not a small inline, the common
> workaround is to add a function call that calls a wrapper function in a
> C file that then calls the tracepoint. But as function calls add overhead,
> this function should only be called when the tracepoint in question is
> enabled. To get around this overhead, a static_branch can be used to only
> have the tracepoint wrapper get called when the tracepoint is enabled.
> 
> Add a tracepoint_enabled(tp) macro that gets passed the name of the
> tracepoint, and this becomes a static_branch that is enabled when the
> tracepoint is enabled and is a nop when the tracepoint is disabled.
> 
> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

Nice! I'm late here, but you mentioned a v3, so FWIW:

Acked-by: Vlastimil Babka <vbabka@...e.cz>