linux-kernel - Re: [PATCHv11 2.6.36-rc2-tip 5/15] 5: uprobes: Uprobes (un)registration and exception handling.

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Message-ID: <20100907120258.GK14891@linux.vnet.ibm.com>
Date:	Tue, 7 Sep 2010 17:32:58 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Mark Wielaard <mjw@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Naren A Devaiah <naren.devaiah@...ibm.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Subject: Re: [PATCHv11 2.6.36-rc2-tip 5/15]  5: uprobes: Uprobes
 (un)registration and exception handling.

> On Mon, Sep 06, 2010 at 11:16:42PM +0530, Srikar Dronamraju wrote:
> > > You don't have to, but you can. The problem I have with this stuff is
> > > that it makes the pid thing a primary interface, whereas it should be
> > > one of many filter possibilities.
> > 
> > I think the otherway, 
> > Why instrument a process and filter it out, if we are not interested in it.
> > While instrumenting kernel, we dont have this flexibility. So
> > having a pid based filter is the right thing to do for kernel
> > based tracing.
> > 
> > If we can get the per process based tracing right, we can build
> > higher lever stuff including the file based tracing easily.
> > 
> > All tools/debuggers in the past have all worked with process based
> > tracing.
> 
> I have the feeling that you guys are at least partially talking past
> each other.
> 
> For the "perf probe --add" interface the only sane interface is one by
> filename and then symbol / liner number / etc.

Agree, probing by file name is a requirement and I am working
towards that end.
> 
> But that is just the interface - these probes don't nessecarily have to
> be armed and cause global overhead once they are define.  If the
> implenmentation is smart enough it will defer arming the probe until
> we actually use it, and that will be per-process quite often.

Agree, That why I am trying to build file-based probing on
pid-based probing.

> 
> Which btw, brings up two more issues, one in uprobes and one in perf.
> For one even in userspace I think the dynamic probes will really just
> be the tip of the iceberg and we'll get more bang for the buck from
> static traces, which is something that's no supported in uprobes yet.
> As a start supporting the dtrace-style sdt.h header would be a great
> help, and then we can decide if we need somthing even better on top.

Yes, Static tracing using dtrace style sdt.h is a cool thing to do.
Already SystemTap has this facility. However I think its probably
better done at perf user interface level.

The way I look at it is perf probe decodes the static markers and asks
uprobes to place probepoints over there.
Do you see a different approach? If yes can you tell what you were
looking at?


--
Thanks and Regards
Srikar
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