linux-kernel - Re: [PATCH v4 12/13] fair.c: Use generic rbtree impl in fair scheduler

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Date:	Wed, 27 Jun 2012 14:36:34 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Daniel Santos <daniel.santos@...ox.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Christopher Li <sparse@...isli.org>,
	David Daney <david.daney@...ium.com>,
	David Howells <dhowells@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Ingo Molnar <mingo@...nel.org>, Joe Perches <joe@...ches.com>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	linux-doc@...r.kernel.org, linux-sparse@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Paul Turner <pjt@...gle.com>,
	Pavel Pisa <pisa@....felk.cvut.cz>,
	Richard Weinberger <richard@....at>,
	Rob Landley <rob@...dley.net>,
	Steven Rostedt <rostedt@...dmis.org>,
	Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: [PATCH v4 12/13] fair.c: Use generic rbtree impl in fair
 scheduler

On Tue, 2012-06-26 at 16:59 -0500, Daniel Santos wrote:
> Also, to address why we're not using entity_before (or a less()
> function) directly, there's two main reasons (one that doesn't even
> affect CFS).  The first reason is that an "is equal" evaluation would
> also be required for insertions in trees with unique keys,

Right, I saw that feature in your code, are there any such trees in the
kernel? It would be good to have a kernel code conversion for each
variant your code supports.

>  as well as
> all lookups.  This doesn't doesn't affect CFS because it isn't doing
> lookups (it only cares about leftmost) and duplicate keys are allowed.
> 
Right.. there's that.

Too bad, partial order is slightly cheaper at times. A well, nothing for
it.

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