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

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Message-ID: <20150327130355.GD6895@linux.vnet.ibm.com>
Date:	Fri, 27 Mar 2015 18:33:55 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.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,
	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
Subject: Re: [PATCH V2] sched: Improve load balancing in the presence of idle
 CPUs

> When a CPU is kicked to do nohz idle balancing, it wakes up to do load
> balancing on itself, followed by load balancing on behalf of idle CPUs.
> But it may end up with load after the load balancing attempt on itself.
> This aborts nohz idle balancing. As a result several idle CPUs are left
> without tasks till such a time that an ILB CPU finds it unfavorable to
> pull tasks upon itself. This delays spreading of load across idle CPUs
> and worse, clutters only a few CPUs with tasks.
> 

[..... snipped .... ]

> Fix this, by checking if a CPU was woken up to do nohz idle load
> balancing, before it does load balancing upon itself. This way we allow
> idle CPUs across the system to do load balancing which results in
> quicker spread of load, instead of performing load balancing within the
> local sched domain hierarchy of the ILB CPU alone under circumstances
> such as above.
> 
> Signed-off-by: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
> ---


Looks good to me.

Reviewed-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>

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