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Date:	Thu, 23 Feb 2012 12:26:50 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Cc:	Mike Galbraith <efault@....de>,
	Peter Zijlstra <peterz@...radead.org>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Paul Turner <pjt@...gle.com>
Subject: Re: sched: Avoid SMT siblings in select_idle_sibling() if possible


* Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com> wrote:

> "perf bench sched pipe" was run 10 times and average ops/sec 
> score alongwith std. dev is noted as below.
> 
> 
> 		SD_BALANCE_WAKE		SD_BALANCE_WAKE
> 		 disabled		enabled
> 
> Avg. score	108984.900 		111844.300 (+2.6%)
> std dev		20383.457		21668.604

pro perf tip of the day: did you know that it's possible to run:

  perf stat --repeat 10 --null perf bench sched pipe

and get meaningful, normalized stddev calculations for free:

       5.486491487 seconds time elapsed                                          ( +-  5.50% )

the percentage at the end shows the level of standard deviation.

You can add "--sync" as well, which will cause perf stat to call 
sync() - this gives extra stability of individual iterations and 
makes sure all IO cost is accounted to the right run.

Thanks,

	Ingo
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