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

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Date:	Mon, 06 Sep 2010 20:15:22 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.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 23:16 +0530, Srikar Dronamraju wrote:
> * Peter Zijlstra <peterz@...radead.org> [2010-09-03 19:19:09]:
> 
> > > 
> > > However I would have an issue with making inode based probing the
> > > default.
> > > 1. Making all probing based on inode can be a performance hog.
> > 
> > How so? You can add filters if you want.
> 
> The breakpoint exception and singlestep account for a substaintial
> time
> of the uprobes probe handling. With increasing number of breakpoint
> hits and singlesteps, wouldnt the overall load increase?
> 
You're really not getting it, are you? No, it would result in the exact
same amount of actual breakpoints hit.

> > 
> > > 2. Since unlike kernel space, every process has a different space, so
> > > why would we have to insert breakpoints in each of its process space if
> > > we are not interested in them.
> > 
> > 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.

Creating inode based probes on top of pid based probes is terribly ugly.

>  Just to clarify, I am not looking at probing per task
> but probing per process. So the pid field in uprobe refers to the
> tgid. 

Urgh,.. I really oppose the whole pid-centric thing, if that means
process wide and not per task its even worse.


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