linux-kernel - Re: [patch 2/2] sched: Scale the nohz_tracker logic by making it per NUMA node

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Message-ID: <1260829283.8023.124.camel@laptop>
Date:	Mon, 14 Dec 2009 23:21:23 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	venkatesh.pallipadi@...el.com
Cc:	Gautham R Shenoy <ego@...ibm.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org,
	Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: [patch 2/2] sched: Scale the nohz_tracker logic by making it
 per NUMA node

On Thu, 2009-12-10 at 17:27 -0800, venkatesh.pallipadi@...el.com wrote:
> Having one idle CPU doing the rebalancing for all the idle CPUs in
> nohz mode does not scale well with increasing number of cores and
> sockets. Make the nohz_tracker per NUMA node. This results in multiple
> idle load balancing happening at NUMA node level and idle load balancer
> only does the rebalance domain among all the other nohz CPUs in that
> NUMA node.
> 
> This addresses the below problem with the current nohz ilb logic
> * The lone balancer may end up spending a lot of time doing the
> * balancing on
>   behalf of nohz CPUs, especially with increasing number of sockets and
>   cores in the platform.

If the purpose is to keep sockets idle, doing things per node doesn't
seem like a fine plan, since we're having nodes <= socket machines these
days.



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