linux-kernel - Re: Implement lbr-as-callgraph v9

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Date:	Wed, 13 Aug 2014 09:24:49 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org, namhyung@...nel.org, acme@...nel.org,
	mingo@...nel.org, peterz@...radead.org
Subject: Re: Implement lbr-as-callgraph v9

On Tue, Aug 12, 2014 at 10:55:24PM +0200, Andi Kleen wrote:
> On Tue, Aug 12, 2014 at 03:50:17PM +0200, Jiri Olsa wrote:
> > On Thu, Jul 31, 2014 at 10:17:00AM -0700, Andi Kleen wrote:
> > 
> > SNIP
> > 
> > > v5:
> > > - Rename functions
> > > - Fix gtk build problem
> > > - Fix crash without -g
> > > - Improve error messages
> > > - Improve srcline display in various ways
> > > v6:
> > > - Port to latest perf/core
> > > v7:
> > > - Really port to latest perf/core
> > > v8:
> > > - Rebased on 3.16-rc1
> > > v9: 
> > > - Forward ported to latest tip/perf/core
> > > 
> > > Example output:
> > > 
> > >     % perf record -b -g ./tsrc/tcall
> > 
> > Why do we need the '-g' in here.. '-b' should be enough right?
> > I saw u fill the rest of the backtrace with callchain
> > data (if needed), but thats not necessary right?
> 
> Right now the callgraph processing needs -g to enable itself.
> I didn't try to fix it so far because we likely use -g in these
> situations where --branch-history is useful.
> 
> If you think it's important it could be fixed I think.
> 
> > 
> > 
> > >     [ perf record: Woken up 1 times to write data ]
> > >     [ perf record: Captured and wrote 0.044 MB perf.data (~1923 samples) ]
> > >     % perf report --branch-history
> > 
> > When I captured data like you above and run pure 'perf report'
> > I did not get callchains displayed at all.
> > 
> > Also using 'perf report --branch-history' enables filename:line
> > suffix for callchain regardless of using '-b' for data capture
> 
> That's fine isn't it? If the user specifies that option
> they should have used -b.
> 
> Or do you mean it should only do it for branch entries?
> Right now the callgraph code doesn't distinguish between branch
> entry and callgraph entry, so it can't know. 

my concern was that '--branch-history' is changing report output
even if there's no branch data.. but thats minor one, the bigger
one is this:

> > When I captured data like you above and run pure 'perf report'
> > I did not get callchains displayed at all.

jirka
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