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

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Date:   Tue, 30 Oct 2018 14:28:45 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Daniel Lezcano <daniel.lezcano@...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

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).

-- 
viresh