linux-kernel - Re: "perf hists browser: Support flat callchains" appears to have broken parent reporting

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Message-ID: <20160330141926.GA5242@awork2.anarazel.de>
Date:	Wed, 30 Mar 2016 16:19:26 +0200
From:	Andres Freund <andres@...razel.de>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: "perf hists browser: Support flat callchains" appears to have
 broken parent reporting

On 2016-03-30 10:46:34 -0300, Arnaldo Carvalho de Melo wrote:
> Em Wed, Mar 30, 2016 at 02:34:18PM +0200, Andres Freund escreveu:
> > Hi,
> > 
> > 4b3a3212233a - "perf hists browser: Support flat callchains" seems to
> > have broken callchain display in tui mode when using !flat mode, or at
> > least changed it in an unintended manner.
> 
> humm, at first I thought this would be related to --percent-limit...

I'm not using --percent-limit. Just to be sure, I did explicitly set it
to various values, and it looks unrelated.

> What tree/branch are you using? Can you try pressing 'L' to play with
> the percent limit?

I'm primarily using linus' tree, and bisected the behavioural down to
that individual commit.

It's somewhat weird that --stdio doesn't show the problem, but --tui
does. Hm.

I don't know the perf code at all, but skimming through the commit, the
following hunk looks suspicious:

@@ -263,7 +295,7 @@ static void callchain_node__init_have_children(struct callchain_node *node,
    chain = list_entry(node->val.next, struct callchain_list, list);
    chain->has_children = has_sibling;

-   if (!list_empty(&node->val)) {
+   if (node->val.next != node->val.prev) {
        chain = list_entry(node->val.prev, struct callchain_list, list);
        chain->has_children = !RB_EMPTY_ROOT(&node->rb_root);
    }

Reverting that individual change fixes things.  I'm not actually sure
what the post 4b3a3212233a version actually tests for?

I think that actually explains why stdio works - nodes are always
unfolded in it, thus ->has_children isn't looked at.

Andres