linux-kernel - Re: [RFC/PATCH] perf tools: Introduce perf

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Message-ID: <20151124073435.GD2636@sejong>
Date:	Tue, 24 Nov 2015 16:34:35 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
CC:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Jiri Olsa <jolsa@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Subject: Re: [RFC/PATCH] perf tools: Introduce perf_thread for backtrace

On Mon, Nov 23, 2015 at 06:39:36PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Fri, Nov 20, 2015 at 03:03:03PM +0900, Namhyung Kim escreveu:
> > Backtrace is a crucial info for debugging.  And upcoming refcnt
> > tracking facility also wants to use it.
> > 
> > So instead of relying on glibc's backtrace_symbols[_fd] which misses
> > some (static) functions , use our own symbol searching mechanism.  To
> > do that, add perf_thread global variable to keep its maps and symbols.
> > 
> > The backtrace output from TUI is changed like below.  (I made a key
> > action to generate a segfault for testing):
> 
> This is a really nice use of what we have, I guess we could simplify
> things further, not having to create a struct machine, as we have just
> one thread, and we're not interested in kernel addresses, so no need for
> kmaps, etc.

Yes, I thought about it.  But as adding the perf thread to an existing
machine can affect other thread(s), I didn't do it.  Maybe we can set
the perf threads' machine pointer in a hacky way without adding the
thread into the machine, but I'd rather not doing that too because
it's fragile and current code is simple enough IMHO.


> 
> But as-is it already looks better than what we were using :-)
> 
> I'll try testing it further and will probably switch to using it if
> nobody voices any problem we haven't realised with such approach.

Thank you!
Namhyung
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