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

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Message-ID: <20140604111730.GM29593@e103034-lin>
Date:	Wed, 4 Jun 2014 12:17:30 +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 Tue, Jun 03, 2014 at 03:02:18PM +0100, Vincent Guittot wrote:
> On 3 June 2014 15:22, Morten Rasmussen <morten.rasmussen@....com> wrote:
> > 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.
> 
> That's normal this patchset is necessary but not enough to solve the
> issue you mention. We also need to fix the way the imbalance is
> calculated for such situation. I have planned to push that in another
> patchset in order to not mix too much thing together

Based on the commit messages I was just lead to believe that this was a
self-contained patch set that also addressed issues related to handling
heterogeneous systems. Maybe it would be worth mentioning that this set
is only part of the solution somewhere?

It is a bit unclear to me how these changes, which appear to mainly
improve factoring rt and irq time into cpu_power, will solve the
cpu_power issues related to heterogeneous systems. Can you share your
plans for the follow up patch set? I think it would be better to review
the solution as a whole.

I absolutely agree that the imbalance calculation needs to fixed, but I
don't think the current rq runnable_avg_sum is the right choice for that
purpose for the reasons I pointed out the in other thread.

Morten
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