Message-ID: <47BD4D48.4080606@linux.vnet.ibm.com>
Date: Thu, 21 Feb 2008 15:37:04 +0530
From: Balbir Singh <balbir@linux.vnet.ibm.com>
Reply-To: balbir@linux.vnet.ibm.com
Organization: IBM
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To: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Ingo Molnar <mingo@elte.hu>,
       "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>,
       Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>,
       Dhaval Giani <dhaval@linux.vnet.ibm.com>, linux-kernel@vger.kernel.org
Subject: Re: Make yield_task_fair more efficient
References: <20080221053321.GA26918@balbir.in.ibm.com> <20080221060427.GA9159@elte.hu> <47BD1F75.5030506@linux.vnet.ibm.com> <20080221070733.GA13694@elte.hu> <47BD2A99.3010608@linux.vnet.ibm.com> <1203583439.6243.119.camel@lappy> <47BD3B56.3090404@linux.vnet.ibm.com> <20080221090430.GA20055@elte.hu>  <47BD44FF.7070104@linux.vnet.ibm.com> <1203586980.6243.124.camel@lappy>  <47BD479F.6070901@linux.vnet.ibm.com> <1203588090.6243.128.camel@lappy>
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Peter Zijlstra wrote:
> On Thu, 2008-02-21 at 15:12 +0530, Balbir Singh wrote:
>> Peter Zijlstra wrote:
>>> On Thu, 2008-02-21 at 15:01 +0530, Balbir Singh wrote:
>>>
>>>> I have an alternate approach in mind (that I need to find time for),
>>>> threaded-rbtrees. Walking the tree is really efficient, specially finding
>>>> successor of a node.
>>> Threading the rbtrees would be even more expensive, it would require a
>>> list_head in each node and a full list operation for every tree
>>> operation.
>>>
>> Peter, when I say threaded, I don't mean threaded as in tasks. Please see
>> http://www.nist.gov/dads/HTML/threadedtree.html and
>> http://datastructures.itgo.com/trees/tbt.htm
> 
> I'm quite aware of the meaning of threaded in the context of data
> structures.

Oh! I did not mean to assume anything. Just wanted to make sure we are talking
of the same thing

 They usually require additional list data and operations to
> implement.
> 

>From the definition
A Threaded Binary Tree is a binary tree in which every node that does not have a
right child has a THREAD (in actual sense, a link) to its INORDER successor.

You use the empty pointer (missing right child), so why do we need a list. May
be I am missing something.

> Look at how the latter link you provided grows the rb_node with one
> pointer to provide a single linked list.
> 

Yes, that's a bad example I suppose. Look at
http://www.cs.rutgers.edu/~kaplan/503/thread.html

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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