linux-kernel - Re: [PATCH 3/3] hwmon: (coretemp) Fix core count limitation

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Message-ID: <91a3f785-8d69-4425-ad23-a6ac0ebddb07@roeck-us.net>
Date:   Thu, 30 Nov 2023 19:06:16 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Zhang Rui <rui.zhang@...el.com>, jdelvare@...e.com
Cc:     fenghua.yu@...el.com, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] hwmon: (coretemp) Fix core count limitation

On 11/27/23 05:16, Zhang Rui wrote:
> Currently, coretemp driver only supports 128 cores per package.
> This loses some core temperation information on systems that have more
> than 128 cores per package.
>   [   58.685033] coretemp coretemp.0: Adding Core 128 failed
>   [   58.692009] coretemp coretemp.0: Adding Core 129 failed
> 
> Fix the problem by using a per package list to maintain the per core
> temp_data instead of the fixed length pdata->core_data[] array.
> 
> Signed-off-by: Zhang Rui <rui.zhang@...el.com>
> ---
>   drivers/hwmon/coretemp.c | 110 ++++++++++++++++++---------------------
>   1 file changed, 52 insertions(+), 58 deletions(-)
> 
> diff --git a/drivers/hwmon/coretemp.c b/drivers/hwmon/coretemp.c
> index cef43fedbd58..1bb1a6e4b07b 100644
> --- a/drivers/hwmon/coretemp.c
> +++ b/drivers/hwmon/coretemp.c
> @@ -39,11 +39,7 @@ static int force_tjmax;
>   module_param_named(tjmax, force_tjmax, int, 0444);
>   MODULE_PARM_DESC(tjmax, "TjMax value in degrees Celsius");
>   
> -#define PKG_SYSFS_ATTR_NO	1	/* Sysfs attribute for package temp */
> -#define BASE_SYSFS_ATTR_NO	2	/* Sysfs Base attr no for coretemp */
> -#define NUM_REAL_CORES		128	/* Number of Real cores per cpu */
>   #define CORETEMP_NAME_LENGTH	28	/* String Length of attrs */
> -#define MAX_CORE_DATA		(NUM_REAL_CORES + BASE_SYSFS_ATTR_NO)
>   
>   enum coretemp_attr_index {
>   	ATTR_LABEL,
> @@ -90,17 +86,17 @@ struct temp_data {
>   	struct attribute *attrs[TOTAL_ATTRS + 1];
>   	struct attribute_group attr_group;
>   	struct mutex update_lock;
> +	struct list_head node;
>   };
>   
>   /* Platform Data per Physical CPU */
>   struct platform_data {
>   	struct device		*hwmon_dev;
>   	u16			pkg_id;
> -	u16			cpu_map[NUM_REAL_CORES];
> -	struct ida		ida;
>   	struct cpumask		cpumask;
> -	struct temp_data	*core_data[MAX_CORE_DATA];
>   	struct device_attribute name_attr;
> +	struct mutex		core_data_lock;
> +	struct list_head	core_data_list;
>   };
>   
>   struct tjmax_pci {
> @@ -491,6 +487,23 @@ static struct temp_data *init_temp_data(unsigned int cpu, int pkg_flag)
>   	return tdata;
>   }
>   
> +static struct temp_data *get_tdata(struct platform_data *pdata, int cpu)
> +{
> +	struct temp_data *tdata;
> +
> +	mutex_lock(&pdata->core_data_lock);
> +	list_for_each_entry(tdata, &pdata->core_data_list, node) {
> +		if (cpu >= 0 && !tdata->is_pkg_data && tdata->cpu_core_id == topology_core_id(cpu))
> +			goto found;
> +		if (cpu < 0 && tdata->is_pkg_data)
> +			goto found;
> +	}

I really don't like this. With 128+ cores, it gets terribly expensive.

How about calculating the number of cores in the probe function and
allocating cpu_map[] and core_data[] instead ?

Thanks,
Guenter