linux-kernel - Re: [patch v5 14/15] sched: power aware load balance

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Date:	Fri, 29 Mar 2013 21:39:57 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
CC:	mingo@...hat.com, peterz@...radead.org, efault@....de,
	torvalds@...ux-foundation.org, tglx@...utronix.de,
	akpm@...ux-foundation.org, arjan@...ux.intel.com, bp@...en8.de,
	pjt@...gle.com, namhyung@...nel.org, vincent.guittot@...aro.org,
	gregkh@...uxfoundation.org, viresh.kumar@...aro.org,
	linux-kernel@...r.kernel.org, morten.rasmussen@....com
Subject: Re: [patch v5 14/15] sched: power aware load balance

On 03/29/2013 08:42 PM, Preeti U Murthy wrote:
>> > did you try the simplest benchmark: while true; do :; done
> Yeah I tried out this while true; do :; done benchmark on a vm which ran

Thanks a lot for trying!

What's do you mean 'vm'? Virtual machine?

> on 2 socket, 2 cores each socket and 2 threads each core emulation.
> I ran two instances of this loop with balance policy on, and it was
> found that there was one instance running on each socket, rather than
> both instances getting consolidated on one socket.
> 
> But when I apply the change where we do not consider rq->util if it has
> no nr_running on the rq,the two instances of the above benchmark get
> consolidated onto one socket.
> 
> 

I don't know much of virtual machine, guess the unstable VCPU to CPU pin
cause rq->util keep large? Did you try to pin VCPU to physical CPU?

I still give the rq->util weight even the nr_running is 0, because some
transitory tasks may actived on the cpu, but just missed on balancing point.

I just wondering that forgetting rq->util when nr_running = 0 is the
real root cause if your finding is just on VM and without fixed VCPU to
CPU pin.


-- 
Thanks
    Alex
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