linux-kernel - Re: [PATCH 0/2] ftrace: updates to tip

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Message-ID: <20090116160202.GA15209@elte.hu>
Date:	Fri, 16 Jan 2009 17:02:02 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Chris Mason <chris.mason@...cle.com>
Subject: Re: [PATCH 0/2] ftrace: updates to tip


* Steven Rostedt <rostedt@...dmis.org> wrote:

> 
> On Fri, 16 Jan 2009, Ingo Molnar wrote:
> > > 
> > > But I do notice that not all functions produce a valid stack trace. 
> > > Maybe it would be better to add that api :-?
> > 
> > yes - i think that API would be more intuitive, and that way people could 
> > mix more interesting functions (with stack traces) with less important 
> > functions (no stack traces).
> 
> Ah, that's the point. We can't mix and match on these. Either all 
> functions that are traced do the stack trace, or none do. This is where 
> the new api may be confusing. [...]

that would be confusing indeed.

> [...] We can register a function to be traced via the function pointer, 
> and we can pick which functions to trace, but we can not separate out 
> different functions for different traces.

Why not? We could have a hash of all traced functions with metadata 
attached. Since patching functions in/out would be a relatively rare 
operation, this would be a highly efficient read-mostly hash.

	Ingo
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