Re: [GIT PULL 00/21] perf/core improvements and fixes

[Namhyung Kim]

Hi Arnaldo,

On Fri,  9 Nov 2012 18:42:49 -0300, Arnaldo Carvalho de Melo wrote:
> Hi Ingo,
>
> 	Please consider pulling.
>
> - Arnaldo
>
> The following changes since commit 8dfec403e39b7c37fd6e8813bacc01da1e1210ab:
>
>   perf tests: Removing 'optional' field (2012-11-05 14:03:59 -0300)
>
> are available in the git repository at:
>
>   git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux tags/perf-core-for-mingo
>
> for you to fetch changes up to 27f94d52394003d444a383eaf8d4824daf32432e:
>
>   tools lib traceevent: Use 'const' in variables pointing to const strings (2012-11-09 17:42:47 -0300)
>
> ----------------------------------------------------------------
> perf/core improvements and fixes:
>
> . Add a 'link' method for hists, so that we can have the leader with
>   buckets for all the entries in all the hists.  This new method
>   is now used in the default 'diff' output, making the sum of the 'baseline'
>   column be 100%, eliminating blind spots. Now we need to use this
>   for 'diff' with > 2 perf.data files and for multi event 'report' and
>   'annotate'.

I'm not sure it can be used for group report at least in its current
form.  IIUC it connects multiple hist entries using a list head and
create a dummy entry in the leader if need be.  But it didn't handle
non-leader entries so it's hard to tell which is which if less entries
are present only.  For example consider following case:

	leader		member1		member2
	A		A		A
	B
			C
					D

where leader, member1 and member2 are evsel/hists and A, B, C and D are
hist entries.  After 'linking' the entries the leader will have
following linkage:

	leader
	A	->	A	->	A
	B
	C (dummy) ->	C
	D (dummy)		->	D

In this case, for entry A the leader can determine which entry came from
which hists by looking its order in the list.  For entry B the leader
can use zero value for them since the list is empty.  However for
entries C and D, it cannot know which one is the right hists unless it
records a hist index or creates dummy entry and insert it in a correct
order (looks far from an optimal solution).  Am I missing something?

Thanks,
Namhyung
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