linux-kernel - Re: [ANNOUNCE] New utility: 'trace'

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Date:	Wed, 17 Nov 2010 14:10:13 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Török Edwin <edwintorok@...il.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [ANNOUNCE] New utility: 'trace'

On Wed, 2010-11-17 at 15:05 +0200, Török Edwin wrote:
> On Wed, 17 Nov 2010 13:51:52 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Wed, 2010-11-17 at 14:47 +0200, Török Edwin wrote:
> > > I see --call-graph in the trace record -h output, but it doesn't
> > > seem to work on x86_64 for me.
> > 
> > If you want to unwind userspace you need to build everything with
> > framepointers -- sadly some people have been lobbying to remove
> > framepointers from all distro builds, even though on x86_64 its nearly
> > free (i386 does have a significant performance benefit, sadly).
> > 
> > There's some work on-going to simply copy out the top of stack and let
> > dwarves go wild at it in userspace, but that isn't done yet.
> 
> Even without frame-pointers I should see at least the first caller in
> userspace, since that can be obtained by reading the return address of
> the syscall, right?

Right.

> I don't see any difference in the output of 'trace report' thats why
> I'm asking it is implemented at all right now, or I need additional
> flags to see it.

Ah, I haven't actually looked at any of the perf-trace code yet, so I'm
afraid I can't answer that particular question.

> I do see some difference in output of 'perf record -g/perf report'
> though.

ok.


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