linux-kernel - Re: [PATCH 1/2] tracepoints: Add helper to test if tracepoint is enabled in a header

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Date:   Fri, 25 Sep 2020 13:05:44 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     rostedt <rostedt@...dmis.org>
Cc:     paulmck <paulmck@...nel.org>,
        Michael Jeanson <mjeanson@...icios.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Yafang Shao <laoar.shao@...il.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        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 1/2] tracepoints: Add helper to test if tracepoint is
 enabled in a header

----- On Sep 25, 2020, at 12:26 PM, rostedt rostedt@...dmis.org wrote:

> On Fri, 25 Sep 2020 11:30:06 -0400 (EDT)
> Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:
> 
>> > Anyway, I don't see any issues with the current patch set as is
>> > (besides the documentation fix, which I already updated locally). And
>> > will add this to my queue for linux-next.
>> 
>> The only thing I would change in the documentation is to word this as
>> "here is a trampoline trick which can be used to work-around rare cases
>> of tracepoint header circular dependency issues" rather than "always use
>> this when instrumenting a header".
>> 
> 
> I rather not have tracepoints in headers. Period!
> 
> It's not just about circular dependencies, it also bloats the code.

Fair enough. We could indeed argue that having a tracepoint in a header's
static inline function will end up replicating that tracepoint at every
site where the function is used. So in terms of code size, it's better
to use the trampoline approach.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com