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

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Message-ID: <20150327070008.GA5496@kernel>
Date:	Fri, 27 Mar 2015 15:00:08 +0800
From:	Wanpeng Li <wanpeng.li@...ux.intel.com>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Jason Low <jason.low2@...com>,
	Wanpeng Li <wanpeng.li@...ux.intel.com>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	peterz@...radead.org, mingo@...nel.org, riel@...hat.com,
	daniel.lezcano@...aro.org, vincent.guittot@...aro.org,
	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
Subject: Re: [PATCH V2] sched: Improve load balancing in the presence of idle
 CPUs

Hi Srikar,
On Fri, Mar 27, 2015 at 11:09:07AM +0530, Srikar Dronamraju wrote:
>
>Yes, the need_resched() in nohz_idle_balance() would exit the
>nohz_idle_balance if it has something to run. However I wonder if we
>should move the need_resched check out of the for loop. i.e the
>need_resched check should probably be there with the idle check.
>
>With the current code when the ilb cpus are not free: 
>- We would be updating the nohz.next_balance even through we havent done
>  any load balance.
>- We might iterate thro the nohz.idle_cpus_mask()s to find balance_cpus.

Good idea, the nohz load balance will be delay since nohz.next_balance is 
updated inapposite when current ILB just be busy. I will send a patch to 
fix it. ;)

Regards,
Wanpeng Li 
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