linux-kernel - Re: sched: Consequences of integrating the Per Entity Load Tracking Metric into the Load Balancer

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Date:	Mon, 21 Jan 2013 11:26:00 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
CC:	Vincent Guittot <vincent.guittot@...aro.org>,
	Mike Galbraith <bitbucket@...ine.de>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"svaidy@...ux.vnet.ibm.com" <svaidy@...ux.vnet.ibm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Amit Kucheria <amit.kucheria@...aro.org>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	Paul McKenney <paul.mckenney@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Ingo Molnar <mingo@...nel.org>, Paul Turner <pjt@...gle.com>,
	Venki Pallipadi <venki@...gle.com>,
	Robin Randhawa <robin.randhawa@....com>,
	Lists linaro-dev <linaro-dev@...ts.linaro.org>
Subject: Re: sched: Consequences of integrating the Per Entity Load Tracking
 Metric into the Load Balancer

On 01/21/2013 10:40 AM, Preeti U Murthy wrote:
> Hi Alex,
> Thank you very much for running the below benchmark on
> blocked_load+runnable_load:) Just a few queries.
> 
> How did you do the wake up balancing? Did you iterate over the L3
> package looking for an idle cpu? Or did you just query the L2 package
> for an idle cpu?
> 

Just used the current select_idle_sibling function, so it search in L3
package.
> I think when you are using blocked_load+runnable_load it would be better
> if we just query the L2 package as Vincent had pointed out because the
> fundamental behind using blocked_load+runnable_load is to keep a steady
> state across cpus unless we could reap the advantage of moving the
> blocked load to a sibling core when it wakes up.
> 
> And the drop of performance is relative to what?

it is 2 VS 3.8-rc3
> 1.Your v3 patchset with runnable_load_avg in weighted_cpu_load().
> 2.Your v3 patchset with runnable_load_avg+blocked_load_avg in
> weighted_cpu_load().
> 
> Are the above two what you are comparing? And in the above two versions
> have you included your [PATCH] sched: use instant load weight in burst
> regular load balance?

no this patch.
> 
> On 01/20/2013 09:22 PM, Alex Shi wrote:
>>>>> The blocked load of a cluster will be high if the blocked tasks have
>>>>> run recently. The contribution of a blocked task will be divided by 2
>>>>> each 32ms, so it means that a high blocked load will be made of recent
>>>>> running tasks and the long sleeping tasks will not influence the load
>>>>> balancing.
>>>>> The load balance period is between 1 tick (10ms for idle load balance
>>>>> on ARM) and up to 256 ms (for busy load balance) so a high blocked
>>>>> load should imply some tasks that have run recently otherwise your
>>>>> blocked load will be small and will not have a large influence on your
>>>>> load balance
>>>
>>> Just tried using cfs's runnable_load_avg + blocked_load_avg in
>>> weighted_cpuload() with my v3 patchset, aim9 shared workfile testing
>>> show the performance dropped 70% more on the NHM EP machine. :(
>>>
>>
>> Ops, the performance is still worse than just count runnable_load_avg.
>> But dropping is not so big, it dropped 30%, not 70%.
>>
> 
> Thank you
> 
> Regards
> Preeti U Murthy
> 


-- 
Thanks
    Alex
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