linux-kernel - Re: [PATCH 4/4] base/drivers/topology: Default dmpis-mhz if they are not set in DT

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Date:   Wed, 21 Nov 2018 23:12:09 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     rjw@...ysocki.net, vincent.guittot@...aro.org,
        linux-kernel@...r.kernel.org,
        Chris Redpath <chris.redpath@...aro.org>,
        Quentin Perret <quentin.perret@...aro.org>,
        Amit Kucheria <amit.kucheria@...aro.org>,
        Nicolas Dechesne <nicolas.dechesne@...aro.org>,
        Niklas Cassel <niklas.cassel@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH 4/4] base/drivers/topology: Default dmpis-mhz if they are
 not set in DT

On 30/10/2018 09:58, Viresh Kumar wrote:
> s/dmpis/dmips/ in $subject
> 
> On 29-10-18, 17:23, Daniel Lezcano wrote:
>> In the case of assymetric SoC with the same micro-architecture, we
> 
>                  asymmetric ?
> 
>> have a group of CPUs with smaller OPPs than the other group. One
>> example is the 96boards dragonboard 820c. There is no dmips/MHz
>> difference between both groups, so no need to specify the values in
>> the DT. Unfortunately, without these defined, there is no scaling
>> capacity comutation triggered, so we need to write
> 
>            computation
> 
>> 'capacity-dmips-mhz' for each CPU with the same value in order to
>> force the scaled capacity computation.
>>
>> Fix this by setting a default capacity to SCHED_CAPACITY_SCALE, if no
>> 'capacity-dmips-mhz' is defined in the DT.
>>
>> This was tested on db820c:
>>  - specified values in the DT (correct results)
>>  - partial values defined in the DT (error + fallback to defaults)
>>  - no specified values in the DT (correct results)
>>
>> correct results are:
>>   cat /sys/devices/system/cpu/cpu*/cpu_capacity
>>    758
>>    758
>>   1024
>>   1024
>>
>>   ... respectively for CPU0, CPU1, CPU2 and CPU3.
>>
>> That reflects the capacity for the max frequencies 1593600 and 2150400.
>>
>> Cc: Chris Redpath <chris.redpath@...aro.org>
>> Cc: Quentin Perret <quentin.perret@...aro.org>
>> Cc: Viresh Kumar <viresh.kumar@...aro.org>
>> Cc: Amit Kucheria <amit.kucheria@...aro.org>
>> Cc: Nicolas Dechesne <nicolas.dechesne@...aro.org>
>> Cc: Niklas Cassel <niklas.cassel@...aro.org>
>> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
>> ---
>>  drivers/base/arch_topology.c | 27 ++++++++++++++++++++++++++-
>>  1 file changed, 26 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
>> index 7311641..7d594a6 100644
>> --- a/drivers/base/arch_topology.c
>> +++ b/drivers/base/arch_topology.c
>> @@ -205,6 +205,21 @@ static struct notifier_block init_cpu_capacity_notifier = {
>>  	.notifier_call = init_cpu_capacity_callback,
>>  };
>>  
>> +static int topology_set_default_capacity(void)
>> +{
>> +	int cpu;
>> +
>> +	raw_capacity = kzalloc(num_possible_cpus() * sizeof(*raw_capacity),
>> +			       GFP_KERNEL);
>> +	if (!raw_capacity)
>> +		return -ENOMEM;
>> +
>> +	for_each_possible_cpu(cpu)
>> +		raw_capacity[cpu] = SCHED_CAPACITY_SCALE;
> 
> This isn't actually required as the value of raw_capacity isn't used
> anymore after this point in code. Rather it is forcefully updated in
> init_cpu_capacity_callback():
> 
> raw_capacity[cpu] = topology_get_cpu_scale(NULL, cpu) *
>                     policy->cpuinfo.max_freq / 1000UL;
> 
> Maybe it is better to allocate raw_capacity once at boot and use
> another global variable as flag (raw_capacity is used as a flag right
> now at many places).

Can we keep the proposed change as is to simply fix the default value?

I want to do a separate change with a raw_capacity rewrite and remove
the workqueue freeing it.


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