Date: Thu, 6 Dec 2007 11:11:12 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
       Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>,
       Arjan van de Ven <arjan@infradead.org>
Subject: Re: [patch-early-RFC 00/10] LTTng architecture dependent
	instrumentation
Message-ID: <20071206101112.GB17299@elte.hu>
References: <20071206025650.451824066@polymtl.ca>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20071206025650.451824066@polymtl.ca>
User-Agent: Mutt/1.5.17 (2007-11-01)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1398
Lines: 35


hi Mathieu,

* Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> wrote:

> Hi,
> 
> Here is the architecture dependent instrumentation for LTTng. [...]

A fundamental observation about markers, and i raised this point many 
many months ago already, so it might sound repetitive, but i'm unsure 
wether it's addressed. Documentation/markers.txt still says:

| * Purpose of markers
|
| A marker placed in code provides a hook to call a function (probe) 
| that you can provide at runtime. A marker can be "on" (a probe is 
| connected to it) or "off" (no probe is attached). When a marker is 
| "off" it has no effect, except for adding a tiny time penalty 
| (checking a condition for a branch) and space penalty (adding a few 
| bytes for the function call at the end of the instrumented function 
| and adds a data structure in a separate section).

could you please eliminate the checking of the flag, and insert a pure 
NOP sequence by default (no extra branches), which is then patched in 
with a function call instruction sequence, when the trace point is 
turned on? (on architectures that have code patching infrastructure - 
such as x86)

	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/