linux-kernel - Re: [RFC PATCH] cpufreq: Calling init() of cpufreq

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Date:   Thu, 22 Mar 2018 11:30:13 +0800
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Shunyong Yang <shunyong.yang@...-semitech.com>
Cc:     rjw@...ysocki.net, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Wang Dongsheng <dongsheng.wang@...-semitech.com>,
        Joey Zheng <yu.zheng@...-semitech.com>
Subject: Re: [RFC PATCH] cpufreq: Calling init() of cpufreq_driver  when
 policy inactive cpu online

On 21-03-18, 18:21, Shunyong Yang wrote:
> When multiple cpus are related in one cpufreq policy, the first online cpu
> will be chosen by default to handle cpufreq operations. In a CPPC case,
> let's take two related cpus, cpu0 and cpu1 as an example.
> 
> After system start, cpu0 is the first online cpu. Cpufreq policy will be
> allocated and init() in cpufreq_driver will be called to initialize cpu0's
> perf capabilities and policy parameters.

Not exactly. The init() is called to initialize stuff for all the CPUs that
should be part of policy->related_cpus after init() has returned. So you should
initialize perf capabilities for all of them.

> When cpu1 is online, current code
> will not call init() in cpufreq_driver as policy has been allocated and
> activated by cpu0. So, cpu1's perf capabilities are not initialized
> (all 0s).
> 
> When cpu0 is offline, policy->cpu will be shifted to cpu1. As cpu1's perf
> capabilities are 0s, speed change will not take effect when setting
> speed.
> 
> This patch adds calling init() of cpufreq_driver when policy inactive cpu
> comes to online.

No CPU should be inactive here, its just that you haven't initialized it
properly.

And we are not going to call init() multiple times for a group of CPUs. That's
not what the purpose of init() is.

-- 
viresh