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

Ilpo Järvinen
2023-11-20T11:15:11Z

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 | 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 */
+ 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);
+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
+ * @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)
+{
+ 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
--
2.30.2