linux-kernel - [RFC PATCH 0/4] sched: remove cpu

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Date:	Fri, 22 Nov 2013 14:37:11 +0800
From:	Alex Shi <alex.shi@...aro.org>
To:	mingo@...hat.com, peterz@...radead.org, morten.rasmussen@....com,
	vincent.guittot@...aro.org, daniel.lezcano@...aro.org,
	fweisbec@...il.com, linux@....linux.org.uk, tony.luck@...el.com,
	fenghua.yu@...el.com, tglx@...utronix.de,
	akpm@...ux-foundation.org, arjan@...ux.intel.com, pjt@...gle.com,
	fengguang.wu@...el.com
Cc:	james.hogan@...tec.com, alex.shi@...aro.org, jason.low2@...com,
	gregkh@...uxfoundation.org, hanjun.guo@...aro.org,
	linux-kernel@...r.kernel.org
Subject: [RFC PATCH 0/4] sched: remove cpu_load decay.

The cpu_load decays on time according past cpu load of rq. New sched_avg decays on tasks' load of time. Now we has 2 kind decay for cpu_load. That is a kind of redundancy. And increase the system load in sched_tick etc.

This patch trying to remove the cpu_load decay. And fixed a nohz_full bug by the way. 

There are 5 load_idx used for cpu_load in sched_domain. busy_idx and idle_idx are not zero usually, but newidle_idx, wake_idx and forkexec_idx are all zero on every arch. A shortcut to remove cpu_Load decay in the first patch. just one line patch for this change. :)

I have tested the patchset on my pandaES board, 2 cores ARM Cortex A9.
hackbench thread/pipe performance increased nearly 10% with this patchset! That do surprise me!

	latest kernel 527d1511310a89		+ this patchset
hackbench -T -g 10 -f 40
	23.25"					21.7"
	23.16"					19.99"
	24.24"					21.53"
hackbench -p -g 10 -f 40
	26.52"					22.48"
	23.89"					24.00"
	25.65"					23.06"
hackbench -P -g 10 -f 40
	20.14"					19.37"
	19.96"					19.76"
	21.76"					21.54"

The git tree for this patchset at:
 git@...hub.com:alexshi/power-scheduling.git no-load-idx 
Since Fengguang had included this tree into his kernel testing system. and I haven't get a regression report until now. I suppose it is fine for x86 system.

But anyway, since the scheduler change will effect all archs. and hackbench is only benchmark I found now for this patchset. I'd like to see more testing and talking on this patchset.

Regards
Alex

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