linux-kernel - Re: sched: Improve load balancing in the presence of idle CPUs

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Message-ID: <1428449300.2556.79.camel@j-VirtualBox>
Date:	Tue, 07 Apr 2015 16:28:20 -0700
From:	Jason Low <jason.low2@...com>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Cc:	Morten Rasmussen <morten.rasmussen@....com>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	"riel@...hat.com" <riel@...hat.com>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	"srikar@...ux.vnet.ibm.com" <srikar@...ux.vnet.ibm.com>,
	"pjt@...gle.com" <pjt@...gle.com>,
	"benh@...nel.crashing.org" <benh@...nel.crashing.org>,
	"efault@....de" <efault@....de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"iamjoonsoo.kim@....com" <iamjoonsoo.kim@....com>,
	"svaidy@...ux.vnet.ibm.com" <svaidy@...ux.vnet.ibm.com>,
	"tim.c.chen@...ux.intel.com" <tim.c.chen@...ux.intel.com>,
	jason.low2@...com
Subject: Re: sched: Improve load balancing in the presence of idle CPUs

On Sat, 2015-04-04 at 15:29 +0530, Preeti U Murthy wrote:

> Solution 1: As exists in the mainline
> Solution 2: nohz_idle_balance(); rebalance_domains() on the ILB CPU
> Solution 3: Above patch.
> 
> I observe that Solution 3 is not as aggressive in spreading load as
> Solution 2. With Solution 2, the load gets spread within the first 3-4
> seconds,

hmm, so 3-4 seconds still sounds like a long time.

> while with Solution3, the load gets spread within the first 6-7
> seconds. I think this is because, the above patch decides to further
> nohz_idle_load_balance() based on the load on the current ILB CPU which
> has most likely pulled just one task.

Okay, so perhaps we can also try continuing nohz load balancing if we
find that there are overloaded CPUs in the system.

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