linux-kernel - Re: [RFC] convert ftrace syscall tracer to TRACE

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Message-ID: <20090509153629.GC29911@redhat.com>
Date:	Sat, 9 May 2009 11:36:29 -0400
From:	"Frank Ch. Eigler" <fche@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Jason Baron <jbaron@...hat.com>, Tom Zanussi <tzanussi@...il.com>,
	linux-kernel@...r.kernel.org, fweisbec@...il.com,
	laijs@...fujitsu.com, rostedt@...dmis.org, peterz@...radead.org,
	mathieu.desnoyers@...ymtl.ca, jiayingz@...gle.com,
	mbligh@...gle.com, roland@...hat.com
Subject: Re: [RFC] convert ftrace syscall tracer to TRACE_EVENT()

Hi -

On Sat, May 09, 2009 at 10:37:37AM +0200, Ingo Molnar wrote:
> [...]
> Firstly, it adds two new tracepoints to every system call. That is 
> unnecessary - we already have the TIF flag based callbacks, and we 
> can use the existing syscall attributes table to get to tracepoints 
> - without slow down (or impacting) the fast path in any way.
> [...]

However, as the TIF_SYSCALL_FTRACE and/or TIF_SYSCALL_TRACE flags are
tied to a single consumer, it would limit the usefulness of the
naturally multiple-client tracepoints, if they were made conditional
on them.  Would you be interested in a proper reference-counting API?

- FChE
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