linux-kernel - Re: [PATCH 2/6] drivers base/arch_topology: frequency-invariant load-tracking support

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Date:   Wed, 14 Jun 2017 09:55:44 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        Russell King - ARM Linux <linux@....linux.org.uk>,
        LAK <linux-arm-kernel@...ts.infradead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Russell King <rmk+kernel@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Juri Lelli <juri.lelli@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Morten Rasmussen <morten.rasmussen@....com>
Subject: Re: [PATCH 2/6] drivers base/arch_topology: frequency-invariant
 load-tracking support

On 06/12/2017 04:27 PM, Vincent Guittot wrote:
> On 8 June 2017 at 09:55, Dietmar Eggemann <dietmar.eggemann@....com> wrote:

Hi Vincent,

Thanks for the review!

[...]

>> @@ -225,8 +265,14 @@ static int __init register_cpufreq_notifier(void)
>>
>>          cpumask_copy(cpus_to_visit, cpu_possible_mask);
>>
>> -       return cpufreq_register_notifier(&init_cpu_capacity_notifier,
>> -                                        CPUFREQ_POLICY_NOTIFIER);
>> +       ret = cpufreq_register_notifier(&init_cpu_capacity_notifier,
>> +                                       CPUFREQ_POLICY_NOTIFIER);
>> +
>> +       if (ret)
> 
> Don't you have to free memory allocated for cpus_to_visit in case of
> errot ? it was not done before your patch as well

Yes, we should free cpus_to_visit if the policy notifier registration
fails. But IMHO also, once the parsing of the capacity-dmips-mhz property
is done. free cpus_to_visit is only used in the notifier call 
init_cpu_capacity_callback() after being allocated and initialized in
register_cpufreq_notifier().

We could add something like this as the first patch of this set. Only
mildly tested on Juno. Juri, what do you think?

Author: Dietmar Eggemann <dietmar.eggemann@....com>
Date:   Tue Jun 13 23:21:59 2017 +0100

    drivers base/arch_topology: free cpumask cpus_to_visit
    
    Free cpumask cpus_to_visit in case registering
    init_cpu_capacity_notifier has failed or the parsing of the cpu
    capacity-dmips-mhz property is done. The cpumask cpus_to_visit is
    only used inside the notifier call init_cpu_capacity_callback.
    
    Reported-by: Vincent Guittot <vincent.guittot@...aro.org>
    Signed-off-by: Dietmar Eggemann <dietmar.eggemann@....com>

diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
index d1c33a85059e..f4832c662762 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -206,6 +206,8 @@ static struct notifier_block init_cpu_capacity_notifier = {
 
 static int __init register_cpufreq_notifier(void)
 {
+       int ret;
+
        /*
         * on ACPI-based systems we need to use the default cpu capacity
         * until we have the necessary code to parse the cpu capacity, so
@@ -221,13 +223,19 @@ static int __init register_cpufreq_notifier(void)
 
        cpumask_copy(cpus_to_visit, cpu_possible_mask);
 
-       return cpufreq_register_notifier(&init_cpu_capacity_notifier,
-                                        CPUFREQ_POLICY_NOTIFIER);
+       ret = cpufreq_register_notifier(&init_cpu_capacity_notifier,
+                                       CPUFREQ_POLICY_NOTIFIER);
+
+       if (ret)
+               free_cpumask_var(cpus_to_visit);
+
+       return ret;
 }
 core_initcall(register_cpufreq_notifier);
 
 static void parsing_done_workfn(struct work_struct *work)
 {
+       free_cpumask_var(cpus_to_visit);
        cpufreq_unregister_notifier(&init_cpu_capacity_notifier,
                                         CPUFREQ_POLICY_NOTIFIER);
 }

>> +               return ret;
>> +
>> +       return cpufreq_register_notifier(&set_freq_scale_notifier,
>> +                                        CPUFREQ_TRANSITION_NOTIFIER);
> 
> Don't you have to unregister the other cpufreq notifier if an error is
> returned and free the mem allocated for cpus_to_visit ?

IMHO, that's not necessary.

The transition notifier works completely independent from the policy
notifier. In case the latter gets registered correctly and the registration
of the former fails, the notifier call of the policy notifier still parses
the capacity-dmips-mhz property information and sets per_cpu(max_freq, cpu).

The notifier call set_freq_scale_callback() of the transition notifier will
not be called so that frequency invariance always returns
SCHED_CAPACITY_SCALE.

After the policy notifier has finished its work, it schedules
parsing_done_work() in which it gets unregistered.

[...]