Re: [PATCH v7 0/8] Tunable sched_mc_power_savings=n

From: Vaidyanathan Srinivasan
Date: Tue Dec 30 2008 - 13:12:13 EST


* Ingo Molnar <mingo@xxxxxxx> [2008-12-30 07:21:39]:

>
> * Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote:
>
> > > > KERNBENCH Runs: make -j4 on a x86 8 core, dual socket quad core cpu
> > > > package system
> > > >
> > > > SchedMC Run Time Package Idle Energy Power
> > > > 0 81.68 52.83% 54.71% 1.00x J 1.00y W
> > > > 1 80.70 36.62% 70.11% 0.95x J 0.96y W
> > > > 2 74.95 19.53% 85.92% 0.90x J 0.98y W
>
> > > Your result is very interesting.
> > > level 2 is more fast and efficient of power.
> > >
> > > What's major contributor to use less time in level 2?
> > > I think it's cache bounce is less time than old.
> > > Is right ?
> >
> > Yes, correct
>
> yes, i too noticed that runtime improved so dramatically: +7.5% on
> kernbench is a _very_ big deal.
>
> So i wanted to ask you to re-test whether this speedup is reproducible,
> and if yes, please check a few other workloads (for example sysbench on
> postgresql / mysqld) and send a patch that changes the
> sched_mc_power_savings default to POWERSAVINGS_BALANCE_WAKEUP (2).

The speedup for kernbench is reproducible. I will post a more
detailed test report on kernbench soon. The power-performance benefit
is for an under-utilised system (nr_cpus/2) run of kernbench which is
very ideal to demonstrate the power savings feature. I will also try
sysbench and update results little later. As Balbir mentioned, I am
on vacation and traveling. I will post more benchmark results as soon
as possible.

--Vaidy
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