linux-kernel - Re: [GIT PULL] tracing: make signal tracepoints more useful

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Date:	Mon, 16 Jan 2012 07:31:10 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Seiji Aguchi <saguchi@...hat.com>,
	linux-kernel@...r.kernel.org,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Subject: Re: [GIT PULL] tracing: make signal tracepoints more useful

On Mon, 2012-01-16 at 08:45 +0100, Ingo Molnar wrote:

> Looks good to me at a first (quick) sight, except this bit 
> which changes the ABI:
> 
> > > 	-       TP_printk("sig=%d errno=%d code=%d comm=%s pid=%d",
> > > 	+       TP_printk("sig=%d errno=%d code=%d comm=%s pid=%d grp=%d res=%d",
> 
> That's not how we change tracepoints generally - we add a new 
> one and eventually phase out the old one. Which apps/tools rely 
> on the old tracepoint? If it's exactly zero apps then we might 
> be able to change it, but this needs to be investigated.

But this tracepoint wasn't changed, it was added on to. There's a
difference. Any tool that uses this (including something like powertop)
should be able to handle it. It should be no different than adding
to /proc/stat. We don't create a new /proc file when adding to it. The
original structure is still intact here.

We really need to get a parsing library out to the public. That would
avoid all these issues as the TRACE_EVENT() was originally designed to.

-- Steve



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