linux-kernel - Re: [RFC 3/4] perf, ftrace: Add new perf ioctl for function trace filter

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Date:	Wed, 10 Aug 2011 16:25:35 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>, a.p.zijlstra@...llo.nl,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC 3/4] perf, ftrace: Add new perf ioctl for function trace
 filter

Again, sorry for the late reply.

On Wed, 2011-07-27 at 14:17 +0200, Jiri Olsa wrote:
> On Tue, Jul 26, 2011 at 03:43:44PM +0200, Frederic Weisbecker wrote:
> 
> SNIP
> 
> > Ideally, the filter engine should split expressions into a tree
> > of ops:
> > 
> > 	ip == func1 + func2 + func3 || ip == func4
> > 
> > should be parsed into:
> > 
> >             ||
> >             /\
> >            /  \
> >           /    \
> >          /      \
> >         ==       ==
> >        /  \     /  \
> >       /    \   ip   \
> >      /      \       func4
> >     ip       +       
> >             / \
> >            /   \
> >           +     \
> >          /  \   func3
> >         /    \
> >     func1   func2
> > 
> > And then pass that to ftrace that interprets that tree
> > by building set of functions on top of each node joined to
> > the other.
> > 
> > But that can be complicated to do, and perhaps a bit of
> > an overkill even for daily use of it.
> > 
> > Having a simple "ip == func + func2 + func3" expression support
> 
> so the '+' is just shortcut for '||' ... like:

Please, lets use something other than '+', as it can also be construed
as addition, and will probably confuse things. Or we change the '==' to
'|=' or something, and then comma separate it?

ip |= func1, func2, func3

Where we can say the '|=' ',' pair is a short cut of multiple a == b
|| ..

-- Steve

> 
> "ip == x1 || ip == x1" AND "ip == x1 + x2" mean the same thing
> 
> if we omit the '+' and keep just the whitespace we could use the function
> name parser as used in set_ftrace_filter interface with no change ;)
> but adding new separator should not be that hard..
> 
> > should be enough I think. And we can reject expressions that don't
> > fit that pattern. Then if it becomes necessary one day to support
> > real expressions there, we can still switch to a real tree.
> > 
> > Does that look sane? 
> 
> I'l make the change and send new version
> 
> thanks,
> jirka


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