linux-kernel - Re: [RFC] perf: Dwarf cfi based user callchains

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Date:	Wed, 13 Oct 2010 11:13:27 -0400
From:	fche@...hat.com (Frank Ch. Eigler)
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Tom Zanussi <tzanussi@...il.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Robert Richter <robert.richter@....com>
Subject: Re: [RFC] perf: Dwarf cfi based user callchains


Frederic Weisbecker <fweisbec@...il.com> writes:

> [...]
> This brings dwarf cfi based callchain for userspace apps that don't have
> frame pointers.

Interesting approach!

> [...]
> - it's slow. A first improvement to make it faster is to support binary
>   search from .eh_frame_hdr. 

In systemtap land, we did find a dramatic improvement from this too.

Have you measured the cost of transcribing of potentially large chunks
of the user stacks?  We did not seriously evaluate this path, since we
encounter megabyte+ stacks in larger userspace apps, and copying THAT
out seemed absurd.


- FChE
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