linux-kernel - Re: [PATCH v6 1/2] powerpc: Detect the presence of big-cores via "ibm,thread-groups"

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Date:   Thu, 9 Aug 2018 06:27:43 -0700
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Michael Neuling <mikey@...ling.org>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com>,
        Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
        "Oliver O'Halloran" <oohall@...il.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Murilo Opsfelder Araujo <muriloo@...ux.ibm.com>,
        Anton Blanchard <anton@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 1/2] powerpc: Detect the presence of big-cores via
 "ibm,thread-groups"

* Gautham R. Shenoy <ego@...ux.vnet.ibm.com> [2018-08-09 11:02:07]:

> 
>  int threads_per_core, threads_per_subcore, threads_shift;
> +bool has_big_cores;
>  cpumask_t threads_core_mask;
>  EXPORT_SYMBOL_GPL(threads_per_core);
>  EXPORT_SYMBOL_GPL(threads_per_subcore);
>  EXPORT_SYMBOL_GPL(threads_shift);
> +EXPORT_SYMBOL_GPL(has_big_cores);

Why do we need EXPORT_SYMBOL_GPL?

>  EXPORT_SYMBOL_GPL(threads_core_mask);
> 
> + *
> + * Returns 0 on success, -EINVAL if the property does not exist,
> + * -ENODATA if property does not have a value, and -EOVERFLOW if the
> + * property data isn't large enough.
> + */
> +int parse_thread_groups(struct device_node *dn,
> +			struct thread_groups *tg)
> +{
> +	unsigned int nr_groups, threads_per_group, property;
> +	int i;
> +	u32 thread_group_array[3 + MAX_THREAD_LIST_SIZE];
> +	u32 *thread_list;
> +	size_t total_threads;
> +	int ret;
> +
> +	ret = of_property_read_u32_array(dn, "ibm,thread-groups",
> +					 thread_group_array, 3);
> +
> +	if (ret)
> +		goto out_err;
> +
> +	property = thread_group_array[0];
> +	nr_groups = thread_group_array[1];
> +	threads_per_group = thread_group_array[2];
> +	total_threads = nr_groups * threads_per_group;
> +

Shouldnt we check for property and nr_groups
If the property is not 1 and nr_groups < 1, we should error out
No point in calling a of_property read if property is not right.


Nit: 
Cant we directly assign to tg->property, and hence avoid local
variables, property, nr_groups and threads_per_group?

> +	ret = of_property_read_u32_array(dn, "ibm,thread-groups",
> +					 thread_group_array,
> +					 3 + total_threads);
> +
> +static inline bool dt_has_big_core(struct device_node *dn,
> +				   struct thread_groups *tg)
> +{
> +	if (parse_thread_groups(dn, tg))
> +		return false;
> +
> +	if (tg->property != 1)
> +		return false;
> +
> +	if (tg->nr_groups < 1)
> +		return false;

Can avoid these check if we can check in parse_thread_groups.

>  /**
>   * setup_cpu_maps - initialize the following cpu maps:
>   *                  cpu_possible_mask
> @@ -457,6 +605,7 @@ void __init smp_setup_cpu_maps(void)
>  	int cpu = 0;
>  	int nthreads = 1;
> 
> diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c
> index 755dc98..f5717de 100644
> --- a/arch/powerpc/kernel/sysfs.c
> +++ b/arch/powerpc/kernel/sysfs.c
> @@ -18,6 +18,7 @@
>  #include <asm/smp.h>
>  #include <asm/pmc.h>
>  #include <asm/firmware.h>
> +#include <asm/cputhreads.h>
> 
>  #include "cacheinfo.h"
>  #include "setup.h"
> @@ -1025,6 +1026,33 @@ static ssize_t show_physical_id(struct device *dev,
>  }
>  static DEVICE_ATTR(physical_id, 0444, show_physical_id, NULL);
> 
> +static ssize_t show_small_core_siblings(struct device *dev,
> +					struct device_attribute *attr,
> +					char *buf)
> +{
> +	struct cpu *cpu = container_of(dev, struct cpu, dev);
> +	struct device_node *dn = of_get_cpu_node(cpu->dev.id, NULL);
> +	struct thread_groups tg;
> +	int i, j;
> +	ssize_t ret = 0;
> +

Here we need to check for validity of dn and error out accordingly.


> +	if (parse_thread_groups(dn, &tg))
> +		return -ENODATA;

Did we miss a of_node_put(dn)?

> +
> +	i = get_cpu_thread_group_start(cpu->dev.id, &tg);
> +
> +	if (i == -1)
> +		return -ENODATA;
> +
> +	for (j = 0; j < tg.threads_per_group - 1; j++)
> +		ret += sprintf(buf + ret, "%d,", tg.thread_list[i + j]);

Here, we are making the assumption that group_start will always be the
first thread in the thread_group. However we didnt make the same
assumption in get_cpu_thread_group_start.