linux-kernel - Re: [PATCH v2 08/11] sched: get CPU's activity statistic

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Message-ID: <538B0F90.8090902@arm.com>
Date:	Sun, 01 Jun 2014 12:33:36 +0100
From:	Dietmar Eggemann <dietmar.eggemann@....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>,
	Morten Rasmussen <Morten.Rasmussen@....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 08/11] sched: get CPU's activity statistic

On 30/05/14 20:20, Vincent Guittot wrote:
> On 30 May 2014 11:50, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
>> On 23/05/14 16:53, Vincent Guittot wrote:
>>> Monitor the activity level of each group of each sched_domain level. The
>>> activity is the amount of cpu_power that is currently used on a CPU or group
>>> of CPUs. We use the runnable_avg_sum and _period to evaluate this activity
>>> level. In the special use case where the CPU is fully loaded by more than 1
>>> task, the activity level is set above the cpu_power in order to reflect the
>>> overload of the CPU
>>>
>>> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
>>
>> [...]
>>
>>>   /*
>>>    * select_task_rq_fair: Select target runqueue for the waking task in domains
>>>    * that have the 'sd_flag' flag set. In practice, this is SD_BALANCE_WAKE,
>>> @@ -5518,6 +5535,7 @@ struct sg_lb_stats {
>>>        unsigned long sum_weighted_load; /* Weighted load of group's tasks */
>>>        unsigned long load_per_task;
>>>        unsigned long group_power;
>>> +     unsigned long group_activity; /* Total activity of the group */
>>>        unsigned int sum_nr_running; /* Nr tasks running in the group */
>>>        unsigned int group_capacity;
>>>        unsigned int idle_cpus;
>>> @@ -5538,6 +5556,7 @@ struct sd_lb_stats {
>>>        struct sched_group *busiest;    /* Busiest group in this sd */
>>>        struct sched_group *local;      /* Local group in this sd */
>>>        unsigned long total_load;       /* Total load of all groups in sd */
>>> +     unsigned long total_activity;  /* Total activity of all groups in sd */
>>>        unsigned long total_pwr;        /* Total power of all groups in sd */
>>>        unsigned long avg_load; /* Average load across all groups in sd */
>>>
>>> @@ -5557,6 +5576,7 @@ static inline void init_sd_lb_stats(struct sd_lb_stats *sds)
>>>                .busiest = NULL,
>>>                .local = NULL,
>>>                .total_load = 0UL,
>>> +             .total_activity = 0UL,
>>
>> AFAICS, total_activity is not used right now. Do you intend to use it to
>> calculate something like avg_activity later (like total_load/avg_load)?
>
> this patch only creates group_activity and total_activity.The use of
> these statistics appears on the next patches. I have not planned to
> compute such avg_activity for the moment mainly because i have need it
> yet.
>
> Do you have in mind any use of such avg_activity ?

No, not really but I still don't see (taken all your patches) where 
sds->total_activity is used.

$ find . -name "*.[ch]" | xargs grep total_activity
./kernel/sched/fair.c:	unsigned long total_activity;  /* Total activity 
of all groups in sd */
./kernel/sched/fair.c:		.total_activity = 0UL,
./kernel/sched/fair.c:		sds->total_activity += sgs->group_activity;

OOTH, sgs->group_activity is used to set sgs->group_capacity which is 
then used in if conditions in update_sd_pick_busiest(), 
update_sd_lb_stats() and find_busiest_group().

[...]


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