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

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Date:	Sat, 21 Mar 2009 04:19:54 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Roland McGrath <roland@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>, utrace-devel@...hat.com,
	Frank Eigler <fche@...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

On Sat, 21 Mar 2009 10:12:35 +0100 Ingo Molnar <mingo@...e.hu> wrote:

> 
> * Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > On Sat, 21 Mar 2009 08:43:01 +0100 Ingo Molnar <mingo@...e.hu> wrote:
> > 
> > > 
> > > * Roland McGrath <roland@...hat.com> wrote:
> > > 
> > > > From: Frank Ch. Eigler <fche@...hat.com>
> > > > 
> > > > This is v2 of the prototype utrace-ftrace interface.  This code is 
> > > > based on Roland McGrath's utrace API, which provides programmatic 
> > > > hooks to the in-tree tracehook layer.  This new patch interfaces 
> > > > many of those events to ftrace, as configured by a small number of 
> > > > debugfs controls.  Here's the 
> > > > /debugfs/tracing/process_trace_README:
> > > 
> > > Please submit changes/enhancements to kernel/trace/* to the tracing 
> > > tree maintainers (Steve and me) for review, testing and integration.
> > > 
> > > Please also post patches against the latest tracing tree:
> > > 
> > >    http://people.redhat.com/mingo/tip.git/README
> > 
> > uhm, this patch depends on the (large) utrace patch, which is not 
> > kernel/trace material.
> 
> The thing is, utrace crashes in Fedora have dominated kerneloops.org 
> for many months, so i'm not sure what to make of the idea of posting 
> a 4000+ lines of core kernel code patchset on the last day of the 
> development cycle, a posting that has carefully avoided the Cc:-ing 
> of affected maintainers ;-)
> 
> 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.

> kernel/utrace.c should probably be introduced as 
> kernel/trace/utrace.c not kernel/utrace.c. It also overlaps pending 
> work in the tracing tree and cooperation would be nice and desired.
> 
> The ftrace/utrace plugin is the only real connection utrace has to 
> the mainline kernel, so proper review by the tracing folks and 
> cooperation with the tracing folks is very much needed for the whole 
> thing.

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.

This is all a bit weird.
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