linux-kernel - Re: malloc() tracing in perf?

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Message-Id: <1249558094.32113.242.camel@twins>
Date:	Thu, 06 Aug 2009 13:28:14 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	"Frank Ch. Eigler" <fche@...hat.com>
Cc:	Pekka Enberg <penberg@...helsinki.fi>, Ingo Molnar <mingo@...e.hu>,
	acme <acme@...hat.com>, Steven Rostedt <rostedt@...dmis.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Eduard-Gabriel Munteanu <eduard.munteanu@...ux360.ro>,
	roland <roland@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	linux-kernel@...r.kernel.org
Subject: Re: malloc() tracing in perf?

On Thu, 2009-08-06 at 07:20 -0400, Frank Ch. Eigler wrote:
> Hi -
> 
> On Thu, Aug 06, 2009 at 10:16:50AM +0200, Peter Zijlstra wrote:
> > [...]
> > > But then it hit me, why can't I have kmemtrace + perf but for 
> > > user-space? Something like the "Malloc Trace" shown here:
> > > [...]
> 
> > I seem to have heard people are working on such a thing, but I can't
> > seem to find a single LKML post with 'uprobe' in the subject in the
> > past two years [...]
> 
> That work is ongoing, and being discussed on utrace-devel@...hat.com,
> since it is a prerequisite. 

Still hiding the discussion and the design never helped anybody.

You might think it ready and then post it to LKML only to have it ripped
apart -- have the discussion openly please.

> > Now doing probes on userspace is hard because you need to know more
> > about the userspace bits than a kernel really ought to be interested
> > in.  [...]  Anyway, like you say, it has uses (potentially very
> > powerful ones), Sun/Apple do it with Dtrace, Linux wants it but I
> > don't think we quite agreed on how to do it :-)
> 
> While these deliberations are ongoing, you can use systemtap.  Probing
> random places in userspace is about as casual as probing the kernel:

Right, but that still doesn't tell us anything on how you're doing that,
does it?



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