linux-kernel - Re: RFC: callchain showing same entry as hist

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Message-ID: <20160816153143.GJ20972@kernel.org>
Date:	Tue, 16 Aug 2016 12:31:43 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Jiri Olsa <jolsa@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: RFC: callchain showing same entry as hist_entry

Em Wed, Aug 17, 2016 at 12:23:55AM +0900, Namhyung Kim escreveu:
> On Tue, Aug 16, 2016 at 12:08:03PM -0300, Arnaldo Carvalho de Melo wrote:
> > Em Tue, Aug 16, 2016 at 11:55:11PM +0900, Namhyung Kim escreveu:
> > > 
> > > On Tue, Aug 16, 2016 at 11:36:28AM -0300, Arnaldo Carvalho de Melo wrote:
> > > > 	please take a look at the patch below, and Ack if possible, it
> > > > is a problem introduced in:
> > > > 
> > > >   cfaa154b2335 ("perf tools: Get rid of obsolete hist_entry__sort_list")
> > > > 
> > > > That is not equivalent to the code that was there and results in having
> > > > the same entry as the first entry for the callchain as in the
> > > > hist_entry, which is annoying and doesn't match the original intent of
> > > > that 'continue' branch, as described in the comment right above it.
> > > 
> > > AFAIK the intent was to skip first callchain entry iff the first sort
> > > key is 'symbol'.  The sort_order being NULL means it'd use the default
> > > sort key which is 'comm,dso,sym' so it should not skip the first
> > > callchain entry.
> > > 
> > > The original code (before cfaa154b2335) was like below:
> > > 
> > > -                       if (!i++ && sort__first_dimension == SORT_SYM)
> > > +                       if (!i++ && field_order == NULL &&
> > > +                           sort_order && !prefixcmp(sort_order, "sym"))
> > > 
> > > I think the current code works as intended, no?
> > 
> > Well, see below the cset comment (local one, will change as we discuss),
> > may clarify further, but yeah, we can't take for granted that the
> > default sort order has "sym" in it :-\
> > 
> > So the original intent description was ambiguous, what we want to avoid
> > is what is in the cset comment below, so the logic for that should be a
> > bit different, tho.
> > 
> > For starters we need to have a callchain_something__first() that will
> > skip the first one using this logic and then use it in all places in
> > --stdio, --tui, --gtk where we need this.
> > 
> > commit c066eaa8d06b87c77b82d55bbc59be308aca4684
> > Author: Arnaldo Carvalho de Melo <acme@...hat.com>
> > Date:   Tue Aug 16 11:36:50 2016 -0300
> > 
> >     perf callchain: Do not repeat the hist_entry symbol as the 1st callchain entry
> >     
> >     We were getting:
> >     
> >          2.62%  [k] __d_lookup_rcu
> >                 |
> >                 ---__d_lookup_rcu
> >                    |
> >                     --2.52%--lookup_fast
> >                               |
> >                                --2.50%--walk_component
> >     
> >     Noticed the __d_lookup_rcu dup, when the original coder intent, and the saner
> >     output is:
> >     
> >          2.62%  [k] __d_lookup_rcu
> >                 |
> >                  --2.52%--lookup_fast
> >                            |
> >                             --2.50%--walk_component
> >     
> >     This is for --stdio, TUI being investigated.
> 
> Did you run 'perf report -s sym --stdio'?  It seems that current code
> already works as sane..  Do you want to make it work for the default sort
>> key too?

What I want is not to repeat the hist_entry line as the first entry in
the callchain, which is confusing.

I.e. repeat the duplication that is happening with the default sort
entry, that contains "sym".

- Arnaldo