linux-kernel - Re: [PATCH v2 04/11] sched: Allow all archs to set the power

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Date:	Tue, 3 Jun 2014 14:22:18 +0100
From:	Morten Rasmussen <morten.rasmussen@....com>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	"peterz@...radead.org" <peterz@...radead.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"preeti@...ux.vnet.ibm.com" <preeti@...ux.vnet.ibm.com>,
	"efault@....de" <efault@....de>,
	"nicolas.pitre@...aro.org" <nicolas.pitre@...aro.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>
Subject: Re: [PATCH v2 04/11] sched: Allow all archs to set the power_orig

On Fri, May 23, 2014 at 04:52:58PM +0100, Vincent Guittot wrote:
> power_orig is only changed for system with a SMT sched_domain level in order to
> reflect the lower capacity of CPUs. Heterogenous system also have to reflect an
> original capacity that is different from the default value.
> 
> Create a more generic function arch_scale_cpu_power that can be also used by
> non SMT platform to set power_orig.

I did a quick test of the patch set with adjusting cpu_power on
big.LITTLE (ARM TC2) to reflect the different compute capacities of the
A15s and A7s. I ran the sysbench cpu benchmark with 5 threads with and
without the patches applied, but with non-default cpu_powers.

I didn't see any difference in the load-balance. Three tasks ended up on
the two A15s and two tasks ended up on two of the three A7s leaving one
unused in both cases.

Using default cpu_power I get one task on each of the five cpus (best
throughput). Unless I messed something up, it seems that setting
cpu_power doesn't give me the best throughput with these patches
applied.

Have you done any tests on big.LITTLE?

Morten
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