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

From:  "Frank Ch. Eigler" <fche-AT-redhat.com>
To:  Andrew Morton <akpm-AT-linux-foundation.org>
Subject:  Re: [PATCH 3/3] utrace-based ftrace "process" engine, v2
Date:  Sat, 21 Mar 2009 07:51:41 -0400
Message-ID:  <20090321115141.GA3566@redhat.com>
Cc:  Peter Zijlstra <a.p.zijlstra-AT-chello.nl>, linux-kernel-AT-vger.kernel.org, Steven Rostedt <rostedt-AT-goodmis.org>, utrace-devel-AT-redhat.com, Linus Torvalds <torvalds-AT-linux-foundation.org>, Thomas Gleixner <tglx-AT-linutronix.de>
Archive-link:  Article

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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