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Date:	Fri, 6 Jun 2014 09:01:54 +0200
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Morten Rasmussen <morten.rasmussen@....com>
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 4 June 2014 13:17, Morten Rasmussen <morten.rasmussen@....com> wrote:
> 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?

So this patch addresses the issue of describing the CPU capacity of an
HMP system but doesn't solve the one task per CPU issue alone.

>
> 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 have planned to use load_per_task to calculate the imbalance to pull

>
> 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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