linux-kernel - Re: [RFCv5 PATCH 16/46] sched: Allocate and initialize energy data structures

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Date:	Wed, 12 Aug 2015 18:09:59 +0100
From:	Dietmar Eggemann <dietmar.eggemann@....com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Morten Rasmussen <Morten.Rasmussen@....com>
CC:	"mingo@...hat.com" <mingo@...hat.com>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
	"yuyang.du@...el.com" <yuyang.du@...el.com>,
	"mturquette@...libre.com" <mturquette@...libre.com>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	Juri Lelli <Juri.Lelli@....com>,
	"sgurrappadi@...dia.com" <sgurrappadi@...dia.com>,
	"pang.xunlei@....com.cn" <pang.xunlei@....com.cn>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [RFCv5 PATCH 16/46] sched: Allocate and initialize energy data
 structures

On 12/08/15 11:17, Peter Zijlstra wrote:
> On Tue, Jul 07, 2015 at 07:23:59PM +0100, Morten Rasmussen wrote:
>> @@ -6647,10 +6703,24 @@ static int __sdt_alloc(const struct cpumask *cpu_map)

[...]

>> @@ -6674,6 +6744,16 @@ static int __sdt_alloc(const struct cpumask *cpu_map)
>>  				return -ENOMEM;
>>  
>>  			*per_cpu_ptr(sdd->sgc, j) = sgc;
>> +
>> +			sge = kzalloc_node(sizeof(struct sched_group_energy) +
>> +				nr_idle_states*sizeof(struct idle_state) +
>> +				nr_cap_states*sizeof(struct capacity_state),
>> +				GFP_KERNEL, cpu_to_node(j));
>> +
>> +			if (!sge)
>> +				return -ENOMEM;
>> +
>> +			*per_cpu_ptr(sdd->sge, j) = sge;
>>  		}
>>  	}
>>  
> 
> One more question, if fn() returns a full structure, why are we
> allocating and copying the thing? Its all const read only data, right?
> 

Yeah, that's not strictly necessary. I could get rid of all the
allocation/copying/ and freeing code and just simply set sd->groups->sge
= fn(cpu) in init_sched_energy(). Plus delete the atomic_t ref in struct
sched_group_energy.

In this case, should I still keep the check_sched_energy_data() function
to verify that the scheduler got valid data via the struct
sched_domain_topology_level table from the arch, i.e. to make sure that
the per-cpu provided sd energy data is consistent for all cpus within
the sched group cpumask?

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