linux-kernel - Re: [PATCH 3/3] utrace-based ftrace "process" engine, v2

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Date:	Sat, 21 Mar 2009 07:51:41 -0400
From:	"Frank Ch. Eigler" <fche@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Roland McGrath <roland@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>, utrace-devel@...hat.com,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 3/3] utrace-based ftrace "process" engine, v2

Hi -

On Sat, Mar 21, 2009 at 04:19:54AM -0700, Andrew Morton wrote:
> [...]
> > Utrace is very much tracing material - without the ftrace plugin the 
> > whole utrace machinery is just something that provides a _ton_ of 
> > hooks to something entirely external: SystemTap mainly.
> 
> Roland's changelogs don't mention systemtap at all afacit.
> That was, umm, major information lossage.

There have been many mixed messages from LKML on the topic - sometimes
mentioning systemtap is forbidden, other times necessary.  Sorry about
that.

There are several non-systemtap clients in existence or under
development.  You've may have heard of the ptrace cleanup, a
multi-client ptrace replacement, an on-the-fly core dumper, the ftrace
widget, user-space probes.  All of these should have somewhat
compelling non-systemtap uses, if that's an important criterion.

> Actually it seems that the whole utrace-ftrace thing is a big
> distraction and could/should just be omitted.  This is a systemtap
> feature and should be viewed as such. [...]

utrace is a better way to perform user thread management than what is
there now, and the utrace-ftrace widget shows how to *hook* thread
events such as syscalls in a lighter weight / more managed way than
the first one proposed.  (That's one reason we've been participating
in the ftrace discussions.)  Of course it can be made to use the fine
syscall pretty-printing code recently added.

- FChE
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