linux-kernel - Re: [PATCH v2 06/13] sched: Store maximum per-cpu capacity in root domain

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Date:	Wed, 13 Jul 2016 14:48:24 +0100
From:	Dietmar Eggemann <dietmar.eggemann@....com>
To:	Vincent Guittot <vincent.guittot@...aro.org>,
	Morten Rasmussen <morten.rasmussen@....com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	Yuyang Du <yuyang.du@...el.com>, mgalbraith@...e.de,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 06/13] sched: Store maximum per-cpu capacity in root
 domain

On 13/07/16 13:40, Vincent Guittot wrote:
> On 22 June 2016 at 19:03, Morten Rasmussen <morten.rasmussen@....com> wrote:
>> From: Dietmar Eggemann <dietmar.eggemann@....com>
>>
>> To be able to compare the capacity of the target cpu with the highest
>> available cpu capacity, store the maximum per-cpu capacity in the root
>> domain.
> 
> I thought that the capacity of all CPUS were built so the highest
> capacity of the CPU of the system is 1024  for big LITTLE system . So
> this patch doesn't seem necessary for big.LITTLE system

The asymmetric cpu capacity support currently only has an effect on arm
big.LITTLE (32bit) using the existing 'struct cpu_efficiency
table_efficiency[]' based approach.

So e.g. on TC2 we have 1441 for highest capacity.

[    0.041007] SMP: Total of 5 processors activated (240.00 BogoMIPS).
[    0.041024] CPU: All CPU(s) started in SVC mode.
[    0.041103] CPU0 attaching sched-domain:
[    0.041119]  domain 0: span 0-1 level MC
[    0.041141]   groups: 0 (cpu_capacity = 1441) 1 (cpu_capacity = 1441)
[    0.041179]   domain 1: span 0-4 level DIE
[    0.041199]    groups: 0-1 (cpu_capacity = 2882) 2-4 (cpu_capacity =
1818)
[    0.041245] CPU1 attaching sched-domain:
[    0.041260]  domain 0: span 0-1 level MC
[    0.041279]   groups: 1 (cpu_capacity = 1441) 0 (cpu_capacity = 1441)
[    0.041315]   domain 1: span 0-4 level DIE
[    0.041334]    groups: 0-1 (cpu_capacity = 2882) 2-4 (cpu_capacity =
1818)
[    0.041376] CPU2 attaching sched-domain:
[    0.041391]  domain 0: span 2-4 level MC
[    0.041409]   groups: 2 (cpu_capacity = 606) 3 (cpu_capacity = 606) 4
(cpu_capacity = 606)
[    0.041460]   domain 1: span 0-4 level DIE
[    0.041479]    groups: 2-4 (cpu_capacity = 1818) 0-1 (cpu_capacity =
2882)
..

[...]