linux-kernel - Re: [PATCH v2 04/26] selftests/resctrl: Refactor get_cbm_mask() and rename to get_full

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Message-ID: <90607b60-b5b0-4dba-b51b-0cd32367d8b2@intel.com>
Date:   Tue, 28 Nov 2023 14:11:05 -0800
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        <linux-kselftest@...r.kernel.org>, Shuah Khan <shuah@...nel.org>,
        "Shaopeng Tan" <tan.shaopeng@...fujitsu.com>,
        Maciej Wieczór-Retman 
        <maciej.wieczor-retman@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>
CC:     <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 04/26] selftests/resctrl: Refactor get_cbm_mask() and
 rename to get_full_cbm()

Hi Ilpo,

On 11/20/2023 3:13 AM, Ilpo Järvinen wrote:
> Callers of get_cbm_mask() are required to pass a string into which the
> capacity bitmask (CBM) is read. Neither CAT nor CMT tests need the
> bitmask as string but just convert it into an unsigned long value.
> 
> Another limitation is that the bit mask reader can only read
> .../cbm_mask files.
> 
> Generalize the bit mask reading function into get_bit_mask() such that
> it can be used to handle other files besides the .../cbm_mask and
> handles the unsigned long conversion within get_bit_mask() using
> fscanf(). Change get_cbm_mask() to use get_bit_mask() and rename it to
> get_full_cbm() to better indicates what the function does.

"to better indicates" -> "to better indicate"

> 
> Also mark cache_type const while at it and remove useless comments that
> are related to processing of CBM bits.
> 
> Co-developed-by: Fenghua Yu <fenghua.yu@...el.com>
> Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> ---

...

> @@ -229,6 +228,32 @@ int get_cbm_mask(char *cache_type, char *cbm_mask)
>  	return 0;
>  }
>  
> +/*
> + * get_full_cbm - Get full Cache Bit Mask (CBM)
> + * @cache_type:	Cache type as "L2" or "L3"
> + * @mask:	Full cache bit mask representing the maximal portion of cache
> + *		available for allocation, returned as unsigned long.
> + *
> + * Return: = 0 on success, < 0 on failure.
> + */
> +int get_full_cbm(const char *cache_type, unsigned long *mask)
> +{
> +	char cbm_path[PATH_MAX];
> +	int ret;
> +
> +	if (!cache_type)
> +		return -1;
> +
> +	snprintf(cbm_path, sizeof(cbm_path), "%s/%s/cbm_mask",
> +		 INFO_PATH, cache_type);
> +
> +	ret = get_bit_mask(cbm_path, mask);
> +	if (ret)
> +		return -1;
> +
> +	return 0;

Can this just be "return get_bit_mask()" ? But actually, I would
like to propose that this also returns a failure if the returned
mask is zero. This would make the code more robust, especially looking
ahead at utility like cache_portion_size() that divides by this full
mask.

Reinette