[PATCH v2 1/2] selftests/resctrl: Adjust effective L3 cache size with SNC enabled

[Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx>]

Sub-NUMA Cluster divides CPUs sharing an L3 cache into separate NUMA
nodes. Systems may support splitting into either two or four nodes.

When SNC mode is enabled the effective amount of L3 cache available
for allocation is divided by the number of nodes per L3.

Detect which SNC mode is active by comparing the number of CPUs
that share a cache with CPU0, with the number of CPUs on node0.

Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
Co-developed-by: Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx>
Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx>
---
 tools/testing/selftests/resctrl/resctrl.h   |  3 ++
 tools/testing/selftests/resctrl/resctrlfs.c | 59 +++++++++++++++++++++
 2 files changed, 62 insertions(+)

diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h
index 00d51fa7531c..3dd5d6779786 100644
--- a/tools/testing/selftests/resctrl/resctrl.h
+++ b/tools/testing/selftests/resctrl/resctrl.h
@@ -11,6 +11,7 @@
 #include <signal.h>
 #include <dirent.h>
 #include <stdbool.h>
+#include <ctype.h>
 #include <sys/stat.h>
 #include <sys/ioctl.h>
 #include <sys/mount.h>
@@ -49,6 +50,7 @@
 		umount_resctrlfs();		\
 		exit(EXIT_FAILURE);		\
 	} while (0)
+#define MAX_SNC		4
 
 /*
  * user_params:		User supplied parameters
@@ -131,6 +133,7 @@ extern pid_t bm_pid, ppid;
 
 extern char llc_occup_path[1024];
 
+int snc_ways(void);
 int get_vendor(void);
 bool check_resctrlfs_support(void);
 int filter_dmesg(void);
diff --git a/tools/testing/selftests/resctrl/resctrlfs.c b/tools/testing/selftests/resctrl/resctrlfs.c
index 1cade75176eb..e4d3624a8817 100644
--- a/tools/testing/selftests/resctrl/resctrlfs.c
+++ b/tools/testing/selftests/resctrl/resctrlfs.c
@@ -156,6 +156,63 @@ int get_domain_id(const char *resource, int cpu_no, int *domain_id)
 	return 0;
 }
 
+/*
+ * Count number of CPUs in a /sys bit map
+ */
+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);
+
+	return count;
+}
+
+/*
+ * Detect SNC by comparing #CPUs in node0 with #CPUs sharing LLC with CPU0.
+ * If some CPUs are offline the numbers may not be exact multiples of each
+ * other. Any offline CPUs on node0 will be also gone from shared_cpu_map of
+ * CPU0 but offline CPUs from other nodes will only make the cache_cpus value
+ * lower. Still try to get the ratio right by preventing the second possibility.
+ */
+int snc_ways(void)
+{
+	int node_cpus, cache_cpus, i;
+
+	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) {
+		fprintf(stderr, "Warning could not determine Sub-NUMA Cluster mode\n");
+		return 1;
+	}
+
+	for (i = 1; i <= MAX_SNC ; i++) {
+		if (i * node_cpus >= cache_cpus)
+			return i;
+	}
+
+	return 1;
+}
+
 /*
  * get_cache_size - Get cache size for a specified CPU
  * @cpu_no:	CPU number
@@ -211,6 +268,8 @@ int get_cache_size(int cpu_no, const char *cache_type, unsigned long *cache_size
 			break;
 	}
 
+	if (cache_num == 3)
+		*cache_size /= snc_ways();
 	return 0;
 }
 
-- 
2.45.0