Re: [RFC] gcc feature request: Moving blocks into sections

From: "H. Peter Anvin" <hpa@linux.intel.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>, gcc <gcc@gcc.gnu.org>,
	Ingo Molnar <mingo@kernel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.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>
Subject: Re: [RFC] gcc feature request: Moving blocks into sections
Date: Mon, 05 Aug 2013 11:17:58 -0700	[thread overview]
Message-ID: <51FFEC56.6040206@linux.intel.com> (raw)
In-Reply-To: <1375725328.22073.101.camel@gandalf.local.home>

On 08/05/2013 10:55 AM, Steven Rostedt wrote:
> 
> Well, as tracepoints are being added quite a bit in Linux, my concern is
> with the inlined functions that they bring. With jump labels they are
> disabled in a very unlikely way (the static_key_false() is a nop to skip
> the code, and is dynamically enabled to a jump).
> 

Have you considered using traps for tracepoints?  A trapping instruction
can be as small as a single byte.  The downside, of course, is that it
is extremely suppressed -- the trap is always expensive -- and you then
have to do a lookup to find the target based on the originating IP.

	-hpa