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Date: Mon, 5 Aug 2013 11:20:29 -0700
Message-ID: <CA+55aFwRHpL-3YObZfw6NxxDxMqQbiwp0=NnpotGj2RHDNF3iw@mail.gmail.com>
Subject: Re: [RFC] gcc feature request: Moving blocks into sections
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: LKML <linux-kernel@vger.kernel.org>, gcc <gcc@gcc.gnu.org>,
        Ingo Molnar <mingo@kernel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        "H. Peter Anvin" <hpa@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        David Daney <ddaney.cavm@gmail.com>,
        Behan Webster <behanw@converseincode.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Herbert Xu <herbert@gondor.hengli.com.au>
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On Mon, Aug 5, 2013 at 10:55 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
>
> My main concern is with tracepoints. Which on 90% (or more) of systems
> running Linux, is completely off, and basically just dead code, until
> someone wants to see what's happening and enables them.

The static_key_false() approach with minimal inlining sounds like a
much better approach overall. Sure, it might add a call/ret, but it
adds it to just the unlikely tracepoint taken path.

Of course, it would be good to optimize static_key_false() itself -
right now those static key jumps are always five bytes, and while they
get nopped out, it would still be nice if there was some way to have
just a two-byte nop (turning into a short branch) *if* we can reach
another jump that way..For small functions that would be lovely. Oh
well.

                Linus
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