linux-kernel - Re: [patch 3/6] sched, nohz: sched group, domain aware nohz idle load balancing

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Message-ID: <1322135629.2921.13.camel@twins>
Date:	Thu, 24 Nov 2011 12:53:49 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Venki Pallipadi <venki@...gle.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Mike Galbraith <efault@....de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Tim Chen <tim.c.chen@...ux.jf.intel.com>, alex.shi@...el.com
Subject: Re: [patch 3/6] sched, nohz: sched group, domain aware nohz idle
 load balancing

On Fri, 2011-11-18 at 15:03 -0800, Suresh Siddha wrote:
> Make nohz idle load balancing more scalabale by using the nr_busy_cpus in
> the struct sched_group_power.
> 
> Idle load balance is kicked on one of the idle cpu's when there is atleast
> one idle cpu and
> 
>  - a busy rq having more than one task or
> 
>  - a busy scheduler group having multiple busy cpus that exceed the sched group
>    power or
> 
>  - for the SD_ASYM_PACKING domain, if the lower numbered cpu's in that
>    domain are idle compared to the busy ones.
> 
> This will help in kicking the idle load balancing request only when
> there is a real imbalance. And once it is mostly balanced, these kicks will
> be minimized.
> 
> These changes helped improve the workload that is context switch intensive
> between number of task pairs by 2x on a 8 socket NHM-EX based system.

OK, but the nohz idle balance will still iterate the whole machine
instead of smaller parts, right?


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