linux-kernel - Re: [RFC PATCH v3 5/5] sched: activate active load balancing in new idle cpus

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Date:	Tue, 11 Nov 2008 14:47:15 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Ingo Molnar <mingo@...e.hu>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Vatsa <vatsa@...ux.vnet.ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>,
	Andi Kleen <andi@...stfloor.org>,
	David Collier-Brown <davecb@....com>,
	Tim Connors <tconnors@...ro.swin.edu.au>,
	Max Krasnyansky <maxk@...lcomm.com>
Subject: Re: [RFC PATCH v3 5/5] sched: activate active load balancing in
 new idle cpus

On Tue, 2008-11-11 at 00:03 +0530, Vaidyanathan Srinivasan wrote:
> Active load balancing is a process by which migration thread
> is woken up on the target CPU in order to pull current
> running task on another package into this newly idle
> package.
> 
> This method is already in use with normal load_balance(),
> this patch introduces this method to new idle cpus when
> sched_mc is set to POWERSAVINGS_BALANCE_WAKEUP.
> 
> This logic provides effective consolidation of short running
> daemon jobs in a almost idle system
> 
> The side effect of this patch may be ping-ponging of tasks
> if the system is moderately utilised. May need to adjust the
> iterations before triggering.

OK, I'm so not getting this patch..

if normal newly idle balancing fails that means the other runqueue has
only a single task on it (or some other really stubborn stuff), so then
you go move that one task that is already running, from one cpu to
another.

_why_?

The only answer I can come up with is that you prefer one cpu's
idle-ness over another - which makes sense, as you try to get whole
packages idle.

But I'm not seeing where that package logic is hidden..

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