linux-kernel - Re: tracepoints for kernel/mutex.c

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Message-ID: <20081017165845.GB12352@redhat.com>
Date:	Fri, 17 Oct 2008 12:58:45 -0400
From:	"Frank Ch. Eigler" <fche@...hat.com>
To:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
Cc:	Jason Baron <jbaron@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, fweisbec@...il.com,
	edwintorok@...il.com, mingo@...e.hu,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: tracepoints for kernel/mutex.c

Hi -

On Fri, Oct 17, 2008 at 12:43:52PM -0400, Mathieu Desnoyers wrote:
> [...]
> > > _IFF_ you want to place tracepoints, get them in the same place as the
> > > lock-dep/stat hooks, that way you get all the locks, not only mutexes.
> > 
> > makes sense. So we could layer lock-dep/stat on top of tracepoints? That
> > would potentially also make lock-dep/stat more dynamic.

> Guys, please, let's focus on the infrastructure to manage trace data
> (timestamping, buffering, event ID, event type management) before
> going any further in the instrumentation direction.  

Any trace data management widget design that precludes connection to
an event source as simple as tracepoints or markers is going to be a
disappointment.

> Otherwise we will end up adding instrumentation in the Linux kernel
> without any in-kernel user [...]

Connecting markers to /proc style text files has been demonstrated in
less than a hundred lines of code.

Plus, Jason's note clearly referred to another in-kernel use of this
instrumentation: the possibility of connecting lockdep via generic
tracepoints in the lock-related code rather than special-purpose
hooks.  One benefit could be being able to compile in lockdep and/or
lockstat by default (activating it via a boot option).  The other
would be of course the concurrent/alternative of the instrumentation
for performance-related purposes.

- FChE
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