linux-kernel - Re: [RFC PATCH v3 1/3] sched: schedule balance map foundation

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Date:	Fri, 22 Feb 2013 11:33:25 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Michael Wang <wangyun@...ux.vnet.ibm.com>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>, Paul Turner <pjt@...gle.com>,
	Mike Galbraith <efault@....de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ram Pai <linuxram@...ibm.com>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [RFC PATCH v3 1/3] sched: schedule balance map foundation

On 02/22/2013 10:53 AM, Michael Wang wrote:
>> > 
>>> >> And the final cost is 3000 int and 1030000 pointer, and some padding,
>>> >> but won't bigger than 10M, not a big deal for a system with 1000 cpu
>>> >> too.
>> > 
>> > Maybe, but quadric stuff should be frowned upon at all times, these
>> > things tend to explode when you least expect it.
>> > 
>> > For instance, IIRC the biggest single image system SGI booted had 16k
>> > cpus in there, that ends up at something like 14+14+3=31 aka as 2G of
>> > storage just for your lookup -- that seems somewhat preposterous.
> Honestly, if I'm a admin who own 16k cpus system (I could not even image
> how many memory it could have...), I really prefer to exchange 2G memory
> to gain some performance.
> 
> I see your point here, the cost of space will grow exponentially, but
> the memory of system will also grow, and according to my understanding ,
> it's faster.

Why not seek other way to change O(n^2) to O(n)?

Access 2G memory is unbelievable performance cost.

There are too many jokes on the short-sight of compute scalability, like
Gates' 64K memory in 2000.

-- 
Thanks Alex
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