linux-kernel - Re: [PATCH v5 11/12] sched: replace capacity

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Date:	Tue, 16 Sep 2014 10:00:58 -0700
From:	Dietmar Eggemann <dietmar.eggemann@....com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Vincent Guittot <vincent.guittot@...aro.org>
CC:	Ingo Molnar <mingo@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	LAK <linux-arm-kernel@...ts.infradead.org>,
	Rik van Riel <riel@...hat.com>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	Mike Galbraith <efault@....de>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH v5 11/12] sched: replace capacity_factor by utilization

On 14/09/14 12:41, Peter Zijlstra wrote:
> On Thu, Sep 11, 2014 at 07:26:48PM +0200, Vincent Guittot wrote:
>> On 11 September 2014 18:15, Peter Zijlstra <peterz@...radead.org> wrote:
>>> On Tue, Aug 26, 2014 at 01:06:54PM +0200, Vincent Guittot wrote:
>>>> +static inline int group_has_free_capacity(struct sg_lb_stats *sgs,
>>>> +                     struct lb_env *env)
>>>>   {
>>>> +     if ((sgs->group_capacity_orig * 100) >
>>>> +                     (sgs->group_utilization * env->sd->imbalance_pct))
>>>> +             return 1;
>>>> +
>>>> +     if (sgs->sum_nr_running < sgs->group_weight)
>>>> +             return 1;
>>>>
>>>> +     return 0;
>>>> +}
>>>>
>>>> +static inline int group_is_overloaded(struct sg_lb_stats *sgs,
>>>> +                     struct lb_env *env)
>>>> +{
>>>> +     if (sgs->sum_nr_running <= sgs->group_weight)
>>>> +             return 0;
>>>>
>>>> +     if ((sgs->group_capacity_orig * 100) <
>>>> +                     (sgs->group_utilization * env->sd->imbalance_pct))
>>>> +             return 1;
>>>>
>>>> +     return 0;
>>>>   }
>>>
>>> I'm confused about the utilization vs capacity_orig. I see how we should
>>
>> 1st point is that I should compare utilization vs capacity and not
>> capacity_orig.
>> I should have replaced capacity_orig by capacity in the functions
>> above when i move the utilization statistic from
>> rq->avg.runnable_avg_sum to cfs.usage_load_avg.
>> rq->avg.runnable_avg_sum was measuring all activity on the cpu whereas
>> cfs.usage_load_avg integrates only cfs tasks
>>
>> With this change, we don't need sgs->group_capacity_orig anymore but
>> only sgs->group_capacity. So sgs->group_capacity_orig can be removed
>> as it's no more used in the code as sg_capacity_factor has been
>> removed
>
> Yes, but.. so I suppose we need to add DVFS accounting and remove
> cpufreq from the capacity thing. Otherwise I don't see it make sense.

My understanding is that uArch scaling of capacacity_orig (therefore of 
capacity too) is done by calling arch_scale_cpu_capacity and frequency 
scaling for capacity is done by calling arch_scale_freq_capacity in 
update_cpu_capacity. I understand that this patch-set does not provide 
an implementation of arch_scale_freq_capacity though.

The uArch and frequency scaling of load & utilization will be added 
later. I know that Morten is currently working on a 'uArch and frequency 
invariant load & utilization tracking' patch-set.

Although I don't know exactly what you mean by DVFS accounting and 
remove cpufreq from the capacity here.

-- Dietmar

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