linux-kernel - Re: [patch v5 06/15] sched: log the cpu utilization at rq

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Message-ID: <512579F6.4080800@intel.com>
Date:	Thu, 21 Feb 2013 09:35:50 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	torvalds@...ux-foundation.org, mingo@...hat.com,
	tglx@...utronix.de, akpm@...ux-foundation.org,
	arjan@...ux.intel.com, bp@...en8.de, pjt@...gle.com,
	namhyung@...nel.org, efault@....de, vincent.guittot@...aro.org,
	gregkh@...uxfoundation.org, preeti@...ux.vnet.ibm.com,
	viresh.kumar@...aro.org, linux-kernel@...r.kernel.org,
	morten.rasmussen@....com
Subject: Re: [patch v5 06/15] sched: log the cpu utilization at rq

On 02/20/2013 11:20 PM, Peter Zijlstra wrote:
> On Wed, 2013-02-20 at 22:33 +0800, Alex Shi wrote:
>>> There's generally a better value than 100 when using computers..
>> seeing
>>> how 100 is 64+32+4.
>>
>> I didn't find a good example for this. and no idea of your suggestion,
>> would you like to explain a bit more?
> 
> Basically what you're doing ends up being fixed point math, using 100 as
> unit is inefficient, pick a power-of-2 and everything reduces to
> bit-shifts.
> 
> http://en.wikipedia.org/wiki/Fixed-point_arithmetic
> 
> So use 128 or 1024 or whatever and you don't need mult and div
> instructions to represent [0,1]
> 

got it. will reconsider this.

-- 
Thanks Alex
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