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: <1283807168.1930.919.camel@laptop>
Date:	Mon, 06 Sep 2010 23:06:08 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	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, 2010-09-06 at 16:40 -0400, Christoph Hellwig wrote:

> 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.

The implementation I outlined a few messages ago, would in fact, as you
suggest, avoid arming things when not needed.


> The other things is that perf currently only supports per-kernel pid
> recording, while we'd really need per Posix process, which may contain
> multiple threads for useful tracing of complex userspace applications.
> I also suspect that this will fit the uprobes model much better given
> that the probes will be in any given address space.

perf does report both:

         *      { u32                   pid, tid; } && PERF_SAMPLE_TID

the pid is the process id (thread group leader like) and tid is the
task/thread id.
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