linux-kernel - Re: [PATCH v8 3.2.0-rc5 9/9] perf: perf interface for uprobes

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Date:	Fri, 13 Jan 2012 10:44:48 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-mm <linux-mm@...ck.org>, Andi Kleen <andi@...stfloor.org>,
	Christoph Hellwig <hch@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Roland McGrath <roland@...k.frob.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Anton Arapov <anton@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	yrl.pp-manager.tt@...achi.com
Subject: Re: [PATCH v8 3.2.0-rc5 9/9] perf: perf interface for uprobes

> 
> I mean that tp->module always !NULL if uprobe, then, we don't need
> to change the code. (thus we can reduce the patch size :))
> 

Agree, the new patch that I sent does this.

> 
> >>> +
> >>> +#define DEFAULT_FUNC_FILTER "!_*"
> >>
> >> This is a hidden rule for users ... please remove it.
> >> (or, is there any reason why we need to have it?)
> >>
> >
> > This is to be in sync with your commit
> > 3c42258c9a4db70133fa6946a275b62a16792bb5
> 
> I see, but that commit also provides filter option for changing
> the function filter. Here, user can not change the filter rule.
> 
> I think, currently, we don't need to filter any function by name
> here, since the user obviously intends to probe given function :)

Actually this was discussed in LKML here
https://lkml.org/lkml/2010/7/20/5, please refer the sub-thread.

Basically without this filter, the list of functions is too large
including labels, weak, and local binding function which arent traced.

We can make this filter settable at a later point of time.

> >
> > If the user provides a symbolic link, convert_name_to_addr would get the
> > target executable for the given executable. This would handy if we were
> > to compare existing probes registered on the same application using a
> > different name (symbolic links). Since you seem to like that we register
> > with the name the user has provided, I will just feed address here.
> 
> Hmm, why do we need to compare the probe points? Of course, event-name
> conflict should be solved, but I think it is acceptable that user puts
> several probes on the same exec:vaddr. Since different users may want
> to use it concurrently bit different ways.
> 

The event-names themselves are generated from the probe points. There is
no problem as such if two or more people use a different symlinks to
create probes. I was just trying to see if we could solve the
inconsitency where we warn a person if he is trying to place a probe on
a existing probe but allow the same if he is trying to place a probe on
a existing probe using a different symlink.

This again I have changed as you suggested in the latest patches that I
sent this week.

-- 
Thanks and Regards
Srikar

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