linux-kernel - Re: [PATCH V3 2/2] base/drivers/arch_topology: Default dmips-mhz if they are not set in DT

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Date:   Mon, 26 Nov 2018 09:52:24 +0000
From:   Quentin Perret <quentin.perret@...aro.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     rjw@...ysocki.net, linux-kernel@...r.kernel.org,
        viresh.kumar@...aro.org, Chris Redpath <chris.redpath@...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 V3 2/2] base/drivers/arch_topology: Default dmips-mhz if
 they are not set in DT

On Monday 26 Nov 2018 at 09:44:21 (+0100), Daniel Lezcano wrote:
> In the case of asymmetric SoC with the same micro-architecture, we
> 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 computation triggered, so we need to write
> 'capacity-dmips-mhz' for each CPU with the same value in order to
> force the scaled capacity computation.
> 
> In order to fix this situation, allocate 'raw_capacity' so the pointer
> is set and the init_cpu_capacity_callback() function can be called.
> 
> 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 | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> index fd5325b..e0c5b60 100644
> --- a/drivers/base/arch_topology.c
> +++ b/drivers/base/arch_topology.c
> @@ -243,9 +243,20 @@ static int __init register_cpufreq_notifier(void)
>  	 * until we have the necessary code to parse the cpu capacity, so
>  	 * skip registering cpufreq notifier.
>  	 */
> -	if (!acpi_disabled || !raw_capacity)
> +	if (!acpi_disabled)
>  		return -EINVAL;
>  
> +	if (!raw_capacity) {
> +
> +		pr_info("cpu_capacity: No capacity defined in DT, set default "
> +		       "values to %ld\n", SCHED_CAPACITY_SCALE);
> +
> +		raw_capacity = kmalloc_array(num_possible_cpus(),
> +					     sizeof(*raw_capacity), GFP_KERNEL);
> +		if (!raw_capacity)
> +			return -ENOMEM;
> +	}
> +
>  	if (!alloc_cpumask_var(&cpus_to_visit, GFP_KERNEL)) {
>  		pr_err("cpu_capacity: failed to allocate memory for cpus_to_visit\n");
>  		return -ENOMEM;
> -- 
> 2.7.4

With this, if the DT is partially filled, we will still do the frequency
scaling thing now right ?

I'm not sure if this is the expected behaviour. If the DT is partially
filled, we probably want to have 1024 of capacity for all CPUs to match
the doc.

Maybe you want to test 'if (!raw_capacity || cap_parsing_failed)' at the
top of topology_parse_cpu_capacity() ?

Thanks,
Quentin