linux-kernel - Re: power increase issue on light load

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Date:	Wed, 29 Jun 2011 11:22:44 +0800
From:	"Alex,Shi" <alex.shi@...el.com>
To:	Nikhil Rao <ncrao@...gle.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"Chen, Tim C" <tim.c.chen@...el.com>,
	"Li, Shaohua" <shaohua.li@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Brown, Len" <len.brown@...el.com>
Subject: Re: power increase issue on light load


> 
> Looking at the schedstat data Alex posted:
> - Distribution of load balances across cores looks about the same.
> - Load balancer does more idle balances on 3.0-rc4 as compared to
> 2.6.39 on SMT and NUMA domains. Busy and newidle balances are a mixed
> bag.
> - I see far fewer affine wakeups on 3.0-rc4 as compared to 2.6.39.
> About half as many affine wakeups on SMT and about a quarter as many
> on NUMA.
> 
> I'm investigating the impact of the load resolution patchset on
> effective load and wake affine calculations. This seems to be the most
> obvious difference from the schedstat data.
> 
> Alex -- I have a couple of questions about your test setup and results.
> - What is the impact on throughput of these benchmarks?

both on bltk-office and light load specpower, 10%/20%/30% load, the
throughput almost have no change on my NHM-EP server and t410 laptop.
> - Would it be possible to get a "perf sched" trace on these two kernels?

I will run the testing again and give you data later. but I didn't find
more useful data in 'perf record -e sched*'. 
> - I'm assuming the three sched domains are SMT, MC and NUMA. Is that
> right? Do you have any powersavings balance or special sched domain
> flags enabled?

Yes, and the sched_mc_power_savings and sched_smt_power_savings were
both set. the NHM-EP domain like below: 

CPU15 attaching sched-domain:
 domain 0: span 7,15 level SIBLING
  groups: 15 (cpu_power = 589) 7 (cpu_power = 589)
  domain 1: span 1,3,5,7,9,11,13,15 level MC
   groups: 7,15 (cpu_power = 1178) 1,9 (cpu_power = 1178) 3,11 (cpu_power = 1178) 5,13 (cpu_power = 1178)
   domain 2: span 0-15 level NODE
    groups: 1,3,5,7,9,11,13,15 (cpu_power = 4712) 0,2,4,6,8,10,12,14 (cpu_power = 4712)

> - Are you using group scheduling? If so, what does your setup look like?

I enabled the FAIR group default. But I have tried to disable it. the
problem is same. so, it isn't related to group. 
> 
> -Thanks,
> Nikhil


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