Re: [PATCH 06/24] selftests/resctrl: Exclude shareable bits from schemata in CAT test

Hi Ilpo,

On 10/24/2023 2:26 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@linux.intel.com

tools/testing/selftests/resctrl/cat_test.c | 12 ++- tools/testing/selftests/resctrl/resctrl.h | 3 + tools/testing/selftests/resctrl/resctrlfs.c | 84 +++++++++++++++++++++ 3 files changed, 95 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/resctrl/cat_test.c b/tools/testing/selftests/resctrl/cat_test.c index 80861c362a53..e5861e7cba7e 100644 --- a/tools/testing/selftests/resctrl/cat_test.c +++ b/tools/testing/selftests/resctrl/cat_test.c @@ -92,13 +92,17 @@ int cat_perf_miss_val(int cpu_no, int n, char *cache_type) unsigned long l_mask, l_mask_1; int ret, pipefd[2], sibling_cpu_no; unsigned long cache_total_size = 0;

• unsigned long long_mask;

• unsigned long full_cache_mask, long_mask;

Please do maintain reverse fir order.

int count_of_bits; char pipe_message; size_t span; /* Get default cbm mask for L3/L2 cache */

• ret = get_cbm_mask(cache_type, &long_mask);

• ret = get_cbm_mask(cache_type, &full_cache_mask);
• if (ret)

• return ret;
  

• /* Get the exclusive portion of the cache */
• ret = get_mask_no_shareable(cache_type, &long_mask); if (ret) return ret;

+/*

• • 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;
• int count = 0;

could count be unsigned int?

• while (val) {

• last_val = val;
  

• val &= (val >> 1);
  

• count++;
  

• }
• if (start) {

• if (count)
  

• 	*start = ffsl(last_val) - 1;
  

• else
  

• 	*start = 0;
  

• }
• return count;

+}

/*

• get_cbm_mask - Get cbm bit mask
• @cache_type: Cache level L2/L3

@@ -253,6 +291,52 @@ int get_cbm_mask(const char *cache_type, unsigned long *mask) return 0; } +/*

• • get_shareable_mask - Get shareable mask from shareable_bits for given cache
• • @cache_type: Cache level L2/L3
• • @shareable_mask: shareable mask returned as unsigned long

A nitpick but please be consistent in starting sentences with capital letter.

• • Return: = 0 on success, < 0 on failure.
• */

+int get_shareable_mask(const char *cache_type, unsigned long *shareable_mask) +{

• char mask_path[1024];
• if (!cache_type)

• return -1;
  

Same question as earlier about error checking.

• 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 CBM mask without shareable_bits for given cache
• • @cache_type: Cache level L2/L3
• • @mask: mask returned as unsigned long

Apart from comment about capital letter this comment does not seem to reveal more about what code does.

• • 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_cbm_mask(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;

+}

Nicely done, thanks.

/*

• get_core_sibling - Get sibling core id from the same socket for given CPU
• @cpu_no: CPU number

Reinette