linux-kernel - Re: [PATCH v2] sched: Accelerate "pick_next

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Date:	Wed, 25 Jan 2012 16:55:34 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Michael Wang <wangyun@...ux.vnet.ibm.com>
Cc:	Xiaotian Feng <xtfeng@...il.com>, ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] sched: Accelerate "pick_next_entity" under special
 condition

On Tue, 2012-01-17 at 11:04 +0800, Michael Wang wrote:
> 
> > Then what if condition 1 is true now?
> 
> We can see in original code, even condition 1 is true, we
> still will use value3 if condition3 is true, like this:
> 
> original:
> 
> condition1      condition3      result
> true            true            value3
> true            false           value1
> 
> That means if condition3 is true, we don't care whether
> condition1 is true or not because we will finally use value3.

Right, so from the original 8 possible states we used to evaluate 3*8 =
24 conditionals. The new code will reduce this to 1*4 + 2*2 + 2*3 = 14.

Now I guess the question is if it matters for the modal or average
state.

I've applied the patch since it can't be worse, but I've no idea if it
matters or not in practice.

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