selftests/resctrl: Create cache_portion_size() helper

CAT and CMT tests calculate size of the cache portion for the n-bits
cache allocation on their own.

Add cache_portion_size() helper that calculates size of the cache
portion for the given number of bits and use it to replace the existing
span calculations. This also prepares for the new CAT test that will
need to determine the size of the cache portion also during results
processing.

Rename also 'cache_size' local variables to 'cache_total_size' to
prevent misinterpretations.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/resctrl/cat_test.c

@@ -91,7 +91,7 @@ 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_size = 0;
+	unsigned long cache_total_size = 0;
 	unsigned long long_mask;
 	int count_of_bits;
 	char pipe_message;
@@ -102,10 +102,10 @@ int cat_perf_miss_val(int cpu_no, int n, char *cache_type)
 		return ret;
 
 	/* Get L3/L2 cache size */
-	ret = get_cache_size(cpu_no, cache_type, &cache_size);
+	ret = get_cache_size(cpu_no, cache_type, &cache_total_size);
 	if (ret)
 		return ret;
-	ksft_print_msg("Cache size :%lu\n", cache_size);
+	ksft_print_msg("Cache size :%lu\n", cache_total_size);
 
 	count_of_bits = count_bits(long_mask);
 
@@ -136,7 +136,7 @@ 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_size * (count_of_bits - n) / count_of_bits;
+	span = cache_portion_size(cache_total_size, l_mask, long_mask);
 	strcpy(param.ctrlgrp, "c2");
 	strcpy(param.mongrp, "m2");
 	strcpy(param.filename, RESULT_FILE_NAME2);
@@ -158,7 +158,7 @@ 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_size * n / count_of_bits;
+		span = cache_portion_size(cache_total_size, l_mask_1, long_mask);
 		strcpy(param.filename, RESULT_FILE_NAME1);
 		param.num_of_runs = 0;
 		param.cpu_no = sibling_cpu_no;

tools/testing/selftests/resctrl/cmt_test.c

@@ -72,7 +72,7 @@ int cmt_resctrl_val(int cpu_no, int n, const char * const *benchmark_cmd)
 {
 	const char * const *cmd = benchmark_cmd;
 	const char *new_cmd[BENCHMARK_ARGS];
-	unsigned long cache_size = 0;
+	unsigned long cache_total_size = 0;
 	unsigned long long_mask;
 	char *span_str = NULL;
 	int count_of_bits;
@@ -83,10 +83,10 @@ int cmt_resctrl_val(int cpu_no, int n, const char * const *benchmark_cmd)
 	if (ret)
 		return ret;
 
-	ret = get_cache_size(cpu_no, "L3", &cache_size);
+	ret = get_cache_size(cpu_no, "L3", &cache_total_size);
 	if (ret)
 		return ret;
-	ksft_print_msg("Cache size :%lu\n", cache_size);
+	ksft_print_msg("Cache size :%lu\n", cache_total_size);
 
 	count_of_bits = count_bits(long_mask);
 
@@ -107,7 +107,7 @@ int cmt_resctrl_val(int cpu_no, int n, const char * const *benchmark_cmd)
 		.setup		= cmt_setup,
 	};
 
-	span = cache_size * n / count_of_bits;
+	span = cache_portion_size(cache_total_size, param.mask, long_mask);
 
 	if (strcmp(cmd[0], "fill_buf") == 0) {
 		/* Duplicate the command to be able to replace span in it */

tools/testing/selftests/resctrl/resctrl.h

@@ -116,4 +116,28 @@ int show_cache_info(unsigned long sum_llc_val, int no_of_bits,
 		    unsigned long max_diff_percent, unsigned long num_of_runs,
 		    bool platform, bool cmt);
 
+/*
+ * cache_portion_size - Calculate the size of a cache portion
+ * @cache_size:		Total cache size in bytes
+ * @portion_mask:	Cache portion mask
+ * @full_cache_mask:	Full Cache Bit Mask (CBM) for the cache
+ *
+ * Return: The size of the cache portion in bytes.
+ */
+static inline unsigned long cache_portion_size(unsigned long cache_size,
+					       unsigned long portion_mask,
+					       unsigned long full_cache_mask)
+{
+	unsigned int bits = count_bits(full_cache_mask);
+
+	/*
+	 * With no bits the full CBM, assume cache cannot be split into
+	 * smaller portions. To avoid divide by zero, return cache_size.
+	 */
+	if (!bits)
+		return cache_size;
+
+	return cache_size * count_bits(portion_mask) / bits;
+}
+
 #endif /* RESCTRL_H */