linux-kernel - Re: [tip:perf/core] perf callchain: Convert children list to rbtree

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Message-ID: <20131023124521.GB3824@infradead.org>
Date:	Wed, 23 Oct 2013 10:45:22 -0200
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	mingo@...nel.org, hpa@...or.com, paulus@...ba.org,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	a.p.zijlstra@...llo.nl, namhyung.kim@....com, namhyung@...nel.org,
	jolsa@...hat.com, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/core] perf callchain: Convert children list to rbtree

Em Wed, Oct 23, 2013 at 12:07:26PM +0100, Frederic Weisbecker escreveu:
> On Wed, Oct 23, 2013 at 12:54:48AM -0700, tip-bot for Namhyung Kim wrote:
> > -#define chain_for_each_child(child, parent)	\
> > -	list_for_each_entry(child, &parent->children, siblings)
> > -
> > -#define chain_for_each_child_safe(child, next, parent)	\
> > -	list_for_each_entry_safe(child, next, &parent->children, siblings)
> 
> We can probably keep these APIs using the rb root iteration code.
> 
> There should be an rb_node_for_each() anyway, and rb_node_for_each_entry(). People
> refused to have to have such an API because they feared it would encourage blind use
> of this O(n log n) iteration. There is plenty of such usecase in practice though, especially
> in perf. So I think we can now start to think about it for real.

I tried introducing one, PeterZ objected, on the grounds you mentioned,
and I still think they are needed, agree with you. Just put a:

/*
   DANGER WILL ROBINSON DANGER

   You should know what you're doing, PeterZ is watching you!

   I CAN NOT ACCEPT THAT PERSON ACTION
*/

or something like that above such helpers ;-)

- Arnaldo
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