linux-kernel - Re: [PATCH V2] sched: Improve load balancing in the presence of idle CPUs

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Message-ID: <20150327021201.GA4491@kernel>
Date:	Fri, 27 Mar 2015 10:12:01 +0800
From:	Wanpeng Li <wanpeng.li@...ux.intel.com>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Cc:	peterz@...radead.org, mingo@...nel.org, riel@...hat.com,
	daniel.lezcano@...aro.org, vincent.guittot@...aro.org,
	srikar@...ux.vnet.ibm.com, pjt@...gle.com,
	benh@...nel.crashing.org, efault@....de,
	linux-kernel@...r.kernel.org, iamjoonsoo.kim@....com,
	svaidy@...ux.vnet.ibm.com, tim.c.chen@...ux.intel.com,
	morten.rasmussen@....com, jason.low2@...com,
	Wanpeng Li <wanpeng.li@...ux.intel.com>
Subject: Re: [PATCH V2] sched: Improve load balancing in the presence of idle
 CPUs

Hi Preeti,
On Thu, Mar 26, 2015 at 06:32:44PM +0530, Preeti U Murthy wrote:
>
>1. An ILB CPU was chosen from the first numa domain to trigger nohz idle
>load balancing [Given the experiment, upto 6 CPUs per core could be
>potentially idle in this domain.]
>
>2. However the ILB CPU would call load_balance() on itself before
>initiating nohz idle load balancing.
>
>3. Given cores are SMT8, the ILB CPU had enough opportunities to pull
>tasks from its sibling cores to even out load.
>
>4. Now that the ILB CPU was no longer idle, it would abort nohz idle
>load balancing

I don't see abort nohz idle load balancing when ILB CPU was no longer idle 
in nohz_idle_balance(), could you explain more in details?

Regards,
Wanpeng Li 
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