linux-kernel - Re: [Questions] How to run 'perf top' on ARM to profile kernel functions with modules loaded

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Date:	Thu, 11 Nov 2010 13:06:16 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Jamie Iles <jamie@...ieiles.com>
Cc:	Ming Lei <tom.leiming@...il.com>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Russell King <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [Questions] How to run 'perf top' on ARM to profile kernel
 functions with modules loaded

On Thu, 2010-11-11 at 09:17 +0000, Jamie Iles wrote:
> On Thu, Nov 11, 2010 at 03:52:07PM +0800, Ming Lei wrote:
> > 2010/11/11 Ming Lei <tom.leiming@...il.com>:
> > > Hi,
> > >
> > > 'perf top' can't display any functions when modules are loaded on ARM.
> > 
> > Sorry, should be can't display any kernel functions when modules are loaded
> > on ARM.
> I've noticed this myself and I spent a bit of time looking into it last week 
> but didn't get too far. I did wonder if it was something to do with the map 
> fixups after loading the modules. If you look at the raw events after a perf 
> record with 'perf report -D' then the last module has a size that takes it to 
> 0xFFFFFFFF which overlaps with the rest of the kernel symbols.
> 
> On x86 it looks like the modules are loaded after the kernel image in VM 
> unlike ARM.

Order shouldn't matter, but that overlap is very likely what kills it.
That module size is buggy.
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