Re: [PATCH v2 07/26] selftests/resctrl: Exclude shareable bits from schemata in CAT test

[Reinette Chatre]

Hi Ilpo,

On 11/20/2023 3:13 AM, Ilpo Järvinen wrote:
> CAT test doesn't take shareable bits into account, i.e., the test might
> be sharing cache with some devices (e.g., graphics).
> 
> Introduce get_mask_no_shareable() and use it to provision an
> environment for CAT test where the allocated LLC is isolated better.
> Excluding shareable_bits may create hole(s) into the cbm_mask, thus add
> a new helper count_contiguous_bits() to find the longest contiguous set
> of CBM bits.
> 
> create_bit_mask() is needed by an upcoming CAT test rewrite so make it
> available in resctrl.h right away.
> 
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
> ---
>  tools/testing/selftests/resctrl/cat_test.c  | 12 ++-
>  tools/testing/selftests/resctrl/resctrl.h   |  3 +
>  tools/testing/selftests/resctrl/resctrlfs.c | 89 +++++++++++++++++++++
>  3 files changed, 100 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/testing/selftests/resctrl/cat_test.c b/tools/testing/selftests/resctrl/cat_test.c
> index cfcdb7bd600f..2c8b37c0a179 100644
> --- a/tools/testing/selftests/resctrl/cat_test.c
> +++ b/tools/testing/selftests/resctrl/cat_test.c
> @@ -89,15 +89,19 @@ void cat_test_cleanup(void)
>  
>  int cat_perf_miss_val(int cpu_no, int n, char *cache_type)
>  {
> +	unsigned long full_cache_mask, long_mask;
>  	unsigned long l_mask, l_mask_1;
>  	int ret, pipefd[2], sibling_cpu_no;
>  	unsigned long cache_total_size = 0;
> -	unsigned long long_mask;
>  	int count_of_bits;
>  	char pipe_message;
>  	size_t span;
>  
> -	ret = get_full_cbm(cache_type, &long_mask);
> +	ret = get_full_cbm(cache_type, &full_cache_mask);
> +	if (ret)
> +		return ret;
> +	/* Get the exclusive portion of the cache */

How about:
	"Get largest contiguous exclusive portion of the cache" ?

> +	ret = get_mask_no_shareable(cache_type, &long_mask);
>  	if (ret)
>  		return ret;
>  
> @@ -136,7 +140,7 @@ int cat_perf_miss_val(int cpu_no, int n, char *cache_type)
>  	/* Set param values for parent thread which will be allocated bitmask
>  	 * with (max_bits - n) bits
>  	 */
> -	span = cache_portion_size(cache_total_size, l_mask, long_mask);
> +	span = cache_portion_size(cache_total_size, l_mask, full_cache_mask);
>  	strcpy(param.ctrlgrp, "c2");
>  	strcpy(param.mongrp, "m2");
>  	strcpy(param.filename, RESULT_FILE_NAME2);
> @@ -158,7 +162,7 @@ int cat_perf_miss_val(int cpu_no, int n, char *cache_type)
>  		param.mask = l_mask_1;
>  		strcpy(param.ctrlgrp, "c1");
>  		strcpy(param.mongrp, "m1");
> -		span = cache_portion_size(cache_total_size, l_mask_1, long_mask);
> +		span = cache_portion_size(cache_total_size, l_mask_1, full_cache_mask);
>  		strcpy(param.filename, RESULT_FILE_NAME1);
>  		param.num_of_runs = 0;
>  		param.cpu_no = sibling_cpu_no;
> diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h
> index 57fe42f4eda2..a911b08fa595 100644
> --- a/tools/testing/selftests/resctrl/resctrl.h
> +++ b/tools/testing/selftests/resctrl/resctrl.h
> @@ -99,7 +99,10 @@ void tests_cleanup(void);
>  void mbm_test_cleanup(void);
>  int mba_schemata_change(int cpu_no, const char * const *benchmark_cmd);
>  void mba_test_cleanup(void);
> +unsigned long create_bit_mask(unsigned int start, unsigned int len);
>  int get_full_cbm(const char *cache_type, unsigned long *mask);
> +int get_shareable_mask(const char *cache_type, unsigned long *shareable_mask);

Does this need to be exported?

> +int get_mask_no_shareable(const char *cache_type, unsigned long *mask);
>  int get_cache_size(int cpu_no, const char *cache_type, unsigned long *cache_size);
>  void ctrlc_handler(int signum, siginfo_t *info, void *ptr);
>  int signal_handler_register(void);
> diff --git a/tools/testing/selftests/resctrl/resctrlfs.c b/tools/testing/selftests/resctrl/resctrlfs.c
> index 1ea610fa65b1..3a9ed918d657 100644
> --- a/tools/testing/selftests/resctrl/resctrlfs.c
> +++ b/tools/testing/selftests/resctrl/resctrlfs.c
> @@ -228,6 +228,44 @@ static int get_bit_mask(const char *filename, unsigned long *mask)
>  	return 0;
>  }
>  
> +/*
> + * create_bit_mask- Create bit mask from start,len pair

Please add a space after the comma.

> + * @start:	LSB of the mask
> + * @len		Number of bits in the mask
> + */
> +unsigned long create_bit_mask(unsigned int start, unsigned int len)
> +{
> +	return ((1UL << len) - 1UL) << start;
> +}
> +
> +/*
> + * count_contiguous_bits - Returns the longest train of bits in a bit mask
> + * @val		A bit mask
> + * @start	The location of the least-significant bit of the longest train
> + *
> + * Return:	The length of the contiguous bits in the longest train of bits
> + */
> +static unsigned int count_contiguous_bits(unsigned long val, unsigned int *start)
> +{
> +	unsigned long last_val;
> +	unsigned int count = 0;
> +
> +	while (val) {
> +		last_val = val;
> +		val &= (val >> 1);
> +		count++;
> +	}
> +
> +	if (start) {
> +		if (count)
> +			*start = ffsl(last_val) - 1;
> +		else
> +			*start = 0;
> +	}
> +
> +	return count;
> +}
> +
>  /*
>   * get_full_cbm - Get full Cache Bit Mask (CBM)
>   * @cache_type:	Cache type as "L2" or "L3"
> @@ -254,6 +292,57 @@ int get_full_cbm(const char *cache_type, unsigned long *mask)
>  	return 0;
>  }
>  
> +/*
> + * get_shareable_mask - Get shareable mask from shareable_bits
> + * @cache_type:		Cache type as "L2" or "L3"
> + * @shareable_mask:	Shareable mask returned as unsigned long
> + *
> + * Return: = 0 on success, < 0 on failure.
> + */
> +int get_shareable_mask(const char *cache_type, unsigned long *shareable_mask)

It looks like this can be static.

> +{
> +	char mask_path[PATH_MAX];
> +
> +	if (!cache_type)
> +		return -1;
> +
> +	snprintf(mask_path, sizeof(mask_path), "%s/%s/shareable_bits",
> +		 INFO_PATH, cache_type);
> +
> +	return get_bit_mask(mask_path, shareable_mask);
> +}
> +
> +/*
> + * get_mask_no_shareable - Get Cache Bit Mask (CBM) without shareable bits
> + * @cache_type:		Cache type as "L2" or "L3"
> + * @mask:		The largest exclusive portion of the cache out of the
> + *			full CBM, returned as unsigned long
> + *
> + * Parts of a cache may be shared with other devices such as GPU. This function
> + * calculates the largest exclusive portion of the cache where no other devices
> + * besides CPU have access to the cache portion.
> + *
> + * Return: = 0 on success, < 0 on failure.
> + */
> +int get_mask_no_shareable(const char *cache_type, unsigned long *mask)
> +{
> +	unsigned long full_mask, shareable_mask;
> +	unsigned int start, len;
> +
> +	if (get_full_cbm(cache_type, &full_mask) < 0)
> +		return -1;
> +	if (get_shareable_mask(cache_type, &shareable_mask) < 0)
> +		return -1;
> +
> +	len = count_contiguous_bits(full_mask & ~shareable_mask, &start);
> +	if (!len)
> +		return -1;
> +
> +	*mask = create_bit_mask(start, len);
> +
> +	return 0;
> +}
> +
>  /*
>   * get_core_sibling - Get sibling core id from the same socket for given CPU
>   * @cpu_no:	CPU number


Reinette