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 11:51:28 -0700	[thread overview]
Message-ID: <51FFF430.1060701@linux.intel.com> (raw)
In-Reply-To: <1375728583.22073.118.camel@gandalf.local.home>

On 08/05/2013 11:49 AM, Steven Rostedt wrote:
> On Mon, 2013-08-05 at 11:29 -0700, H. Peter Anvin wrote:
> 
>> Traps nest, that's why there is a stack.  (OK, so you don't want to take
>> the same trap inside the trap handler, but that code should be very
>> limited.)  The trap instruction just becomes very short, but rather
>> slow, call-return.
>>
>> However, when you consider the cost you have to consider that the
>> tracepoint is doing other work, so it may very well amortize out.
> 
> Also, how would you pass the parameters? Every tracepoint has its own
> parameters to pass to it. How would a trap know what where to get "prev"
> and "next"?
> 

How do you do that now?

You have to do an IP lookup to find out what you are doing.

(Note: I wonder how much the parameter generation costs the tracepoints.)

	-hpa