Re: [PATCH v6 1/2] selftests/resctrl: Adjust effective L3 cache size with SNC enabled

Hi Maciej,

On 12/2/24 3:08 AM, Maciej Wieczor-Retman wrote:

diff --git a/tools/testing/selftests/resctrl/resctrlfs.c b/tools/testing/selftests/resctrl/resctrlfs.c index d38d6dd90be4..50561993d37c 100644 --- a/tools/testing/selftests/resctrl/resctrlfs.c +++ b/tools/testing/selftests/resctrl/resctrlfs.c @@ -13,6 +13,8 @@ #include "resctrl.h" +int snc_unreliable;

static int find_resctrl_mount(char *buffer) { FILE *mounts; @@ -156,6 +158,90 @@ int get_domain_id(const char *resource, int cpu_no, int *domain_id) return 0; } +/*

• • Count number of CPUs in a /sys bitmap
• */

+static unsigned int count_sys_bitmap_bits(char *name) +{

• FILE *fp = fopen(name, "r");
• int count = 0, c;
• if (!fp)

• return 0;
  

• while ((c = fgetc(fp)) != EOF) {

• if (!isxdigit(c))
  

• 	continue;
  

• switch (c) {
  

• case 'f':
  

• 	count++;
  

• case '7': case 'b': case 'd': case 'e':
  

• 	count++;
  

• case '3': case '5': case '6': case '9': case 'a': case 'c':
  

• 	count++;
  

• case '1': case '2': case '4': case '8':
  

• 	count++;
  

• }
  

• }
• fclose(fp);

running this through a syntax checker triggers a couple of complaints due to the missing break statements. I think this can be made more robust by making use of "fallthrough" and "break". It looks like this can be obtained by including linux/compiler.h ... but from what I can tell care should be taken to set the include directory _after_ includink lib.mk so that top_srcdir is set correctly.

• return count;

+}

+static bool cpus_offline_empty(void) +{

• char offline_cpus_str[64];
• FILE *fp;
• fp = fopen("/sys/devices/system/cpu/offline", "r");

Please check fp before use.

• if (fscanf(fp, "%s", offline_cpus_str) < 0) {

This needs something equivalent to 46058430fc5d ("selftests/resctrl: Protect against array overflow when reading strings")

• if (!errno) {
  

• 	fclose(fp);
  

• 	return 1;
  

• }
  

• ksft_perror("Could not read /sys/devices/system/cpu/offline");
  

• }
• fclose(fp);
• return 0;

+}

+/*

• • Detect SNC by comparing #CPUs in node0 with #CPUs sharing LLC with CPU0.
• • If any CPUs are offline declare the detection as unreliable and skip the
• • tests.

nit: "and skip the tests" can be dropped since the function need not make assumption about how callers will use it.

• */

+int snc_nodes_per_l3_cache(void) +{

• int node_cpus, cache_cpus;
• static int snc_mode;
• if (!snc_mode) {

• snc_mode = 1;
  

• if (!cpus_offline_empty()) {
  

• 	ksft_print_msg("Runtime SNC detection unreliable due to offline CPUs.\n");
  

• 	ksft_print_msg("Setting SNC mode to disabled.\n");
  

• 	snc_unreliable = 1;
  

• 	return snc_mode;
  

• }
  

• node_cpus = count_sys_bitmap_bits("/sys/devices/system/node/node0/cpumap");
  

• cache_cpus = count_sys_bitmap_bits("/sys/devices/system/cpu/cpu0/cache/index3/shared_cpu_map");
  

• if (!node_cpus || !cache_cpus) {
  

• 	ksft_print_msg("Could not determine Sub-NUMA Cluster mode.\n");
  

• 	snc_unreliable = 1;
  

• 	return snc_mode;
  

• }
  

• snc_mode = cache_cpus / node_cpus;
  

• if (snc_mode > 1)
  

• 	ksft_print_msg("SNC-%d mode discovered.\n", snc_mode);
  

• }
• return snc_mode;

+}

/*

• get_cache_size - Get cache size for a specified CPU
• @cpu_no: CPU number

@@ -211,6 +297,17 @@ int get_cache_size(int cpu_no, const char *cache_type, unsigned long *cache_size break; }

• /*

• * The amount of cache represented by each bit in the masks
  

• * in the schemata file is reduced by a factor equal to SNC
  

• * nodes per L3 cache.
  

• * E.g. on a SNC-2 system with a 100MB L3 cache a test that
  

• * allocates memory from its local SNC node (default behavior
  

• * without using libnuma) will only see 50 MB llc_occupancy
  

• * with a fully populated L3 mask in the schemata file.
  

• */
  

• if (cache_num == 3)

• *cache_size /= snc_nodes_per_l3_cache();
  

  return 0;

}

Reinette