Message-ID: <3D8C7EEE.7030500@colorfullife.com>
Date: Sat, 21 Sep 2002 16:15:10 +0200
From: Manfred Spraul <manfred@colorfullife.com>
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To: Andries Brouwer <aebr@win.tue.nl>
CC: linux-kernel@vger.kernel.org
Subject: Re: quadratic behaviour
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> Let me repeat this, and call it an observation instead of a question,
> so that you do not think I am in doubt.
> 
> If you have 20000 processes, and do ps, then get_pid_list() will be
> called 1000 times, and the for_each_process() loop will examine
> 10000000 processes.
> 
> Unlike the get_pid() situation, which was actually amortized linear with a very
> small coefficient, here we have a bad quadratic behaviour, still in 2.5.37.
> 
One solution would be to replace the idtag hash with an idtag tree.

Then get_pid_list() could return an array of sorted pids, and finding 
the next pid after unlocking the task_lock would be just a tree lookup 
(find first pid larger than x).

And a sorted tree would make it possible find the next safe range for 
get_pid() with O(N) instead of O(N^2).

--
	Manfred


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