[PATCH v2 0/2] selftests/resctrl: SNC kernel support discovery

[PATCH v2 0/2] selftests/resctrl: SNC kernel support discovery

[Maciej Wieczor-Retman]

Changes v2:
- Removed patches 2 and 3 since now this part will be supported by the
  kernel.

Sub-Numa Clustering (SNC) allows splitting CPU cores, caches and memory
into multiple NUMA nodes. When enabled, NUMA-aware applications can
achieve better performance on bigger server platforms.

SNC support in the kernel is currently in review [1]. With SNC enabled
and kernel support in place all the tests will function normally. There
might be a problem when SNC is enabled but the system is still using an
older kernel version without SNC support. Currently the only message
displayed in that situation is a guess that SNC might be enabled and is
causing issues. That message also is displayed whenever the test fails
on an Intel platform.

Add a mechanism to discover kernel support for SNC which will add more
meaning and certainty to the error message.

Series was tested on Ice Lake server platforms with SNC disabled, SNC-2
and SNC-4. The tests were also ran with and without kernel support for
SNC.

Series applies cleanly on kselftest/next.

[1] https://lore.kernel.org/all/20240503203325.21512-1-tony.luck@intel.com/

Previous versions of this series:
[v1] https://lore.kernel.org/all/cover.1709721159.git.maciej.wieczor-retman@intel.com/

Maciej Wieczor-Retman (2):
  selftests/resctrl: Adjust effective L3 cache size with SNC enabled
  selftests/resctrl: Adjust SNC support messages

 tools/testing/selftests/resctrl/cat_test.c  |   2 +-
 tools/testing/selftests/resctrl/cmt_test.c  |   6 +-
 tools/testing/selftests/resctrl/mba_test.c  |   2 +
 tools/testing/selftests/resctrl/mbm_test.c  |   4 +-
 tools/testing/selftests/resctrl/resctrl.h   |   8 +-
 tools/testing/selftests/resctrl/resctrlfs.c | 131 +++++++++++++++++++-
 6 files changed, 144 insertions(+), 9 deletions(-)

-- 
2.45.0

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

[Maciej Wieczor-Retman]

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@intel.com>
Co-developed-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
---
 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

[PATCH v2 2/2] selftests/resctrl: Adjust SNC support messages

[Maciej Wieczor-Retman]

Resctrl selftest prints a message on test failure that Sub-Numa
Clustering (SNC) could be enabled and points the user to check theirs BIOS
settings. No actual check is performed before printing that message so
it is not very accurate in pinpointing a problem.

Figuring out if SNC is enabled is only one part of the problem, the
other being whether the kernel supports it. As there is no easy
interface that simply states SNC support in the kernel one can find that
information by comparing L3 cache sizes from different sources. Cache
size reported by /sys/devices/system/node/node0/cpu0/cache/index3/size
will always show the full cache size even if it's split by enabled SNC.
On the other hand /sys/fs/resctrl/size has information about L3 size,
that with kernel support is adjusted for enabled SNC.

Add a function to find a cache size from /sys/fs/resctrl/size since
finding that information from the other source is already implemented.

Add a function that compares the two cache sizes and use it to make the
SNC support message more meaningful.

Add the SNC support message just after MBA's check_results() since MBA
shares code with MBM and also can suffer from enabled SNC if there is no
support in the kernel.

Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
---
Changelog v2:
- Move snc_ways() checks from individual tests into
  snc_kernel_support().
- Write better comment for snc_kernel_support().

 tools/testing/selftests/resctrl/cat_test.c  |  2 +-
 tools/testing/selftests/resctrl/cmt_test.c  |  6 +-
 tools/testing/selftests/resctrl/mba_test.c  |  2 +
 tools/testing/selftests/resctrl/mbm_test.c  |  4 +-
 tools/testing/selftests/resctrl/resctrl.h   |  5 +-
 tools/testing/selftests/resctrl/resctrlfs.c | 72 ++++++++++++++++++++-
 6 files changed, 82 insertions(+), 9 deletions(-)

diff --git a/tools/testing/selftests/resctrl/cat_test.c b/tools/testing/selftests/resctrl/cat_test.c
index c7686fb6641a..722b4fcaf788 100644
--- a/tools/testing/selftests/resctrl/cat_test.c
+++ b/tools/testing/selftests/resctrl/cat_test.c
@@ -253,7 +253,7 @@ static int cat_run_test(const struct resctrl_test *test, const struct user_param
 		return ret;
 
 	/* Get L3/L2 cache size */
-	ret = get_cache_size(uparams->cpu, test->resource, &cache_total_size);
+	ret = get_sys_cache_size(uparams->cpu, test->resource, &cache_total_size);
 	if (ret)
 		return ret;
 	ksft_print_msg("Cache size :%lu\n", cache_total_size);
diff --git a/tools/testing/selftests/resctrl/cmt_test.c b/tools/testing/selftests/resctrl/cmt_test.c
index a44e6fcd37b7..0ff232d38c26 100644
--- a/tools/testing/selftests/resctrl/cmt_test.c
+++ b/tools/testing/selftests/resctrl/cmt_test.c
@@ -112,7 +112,7 @@ static int cmt_run_test(const struct resctrl_test *test, const struct user_param
 	if (ret)
 		return ret;
 
-	ret = get_cache_size(uparams->cpu, "L3", &cache_total_size);
+	ret = get_sys_cache_size(uparams->cpu, "L3", &cache_total_size);
 	if (ret)
 		return ret;
 	ksft_print_msg("Cache size :%lu\n", cache_total_size);
@@ -157,8 +157,8 @@ static int cmt_run_test(const struct resctrl_test *test, const struct user_param
 		goto out;
 
 	ret = check_results(&param, span, n);
-	if (ret && (get_vendor() == ARCH_INTEL))
-		ksft_print_msg("Intel CMT may be inaccurate when Sub-NUMA Clustering is enabled. Check BIOS configuration.\n");
+	if (ret && (get_vendor() == ARCH_INTEL) && !snc_kernel_support())
+		ksft_print_msg("Kernel doesn't support Sub-NUMA Clustering but it is enabled. Check BIOS configuration.\n");
 
 out:
 	free(span_str);
diff --git a/tools/testing/selftests/resctrl/mba_test.c b/tools/testing/selftests/resctrl/mba_test.c
index 5d6af9e8afed..74e1ebb14904 100644
--- a/tools/testing/selftests/resctrl/mba_test.c
+++ b/tools/testing/selftests/resctrl/mba_test.c
@@ -161,6 +161,8 @@ static int mba_run_test(const struct resctrl_test *test, const struct user_param
 		return ret;
 
 	ret = check_results();
+	if (ret && (get_vendor() == ARCH_INTEL) && !snc_kernel_support())
+		ksft_print_msg("Kernel doesn't support Sub-NUMA Clustering but it is enabled. Check BIOS configuration.\n");
 
 	return ret;
 }
diff --git a/tools/testing/selftests/resctrl/mbm_test.c b/tools/testing/selftests/resctrl/mbm_test.c
index 3059ccc51a5a..e542938272f9 100644
--- a/tools/testing/selftests/resctrl/mbm_test.c
+++ b/tools/testing/selftests/resctrl/mbm_test.c
@@ -129,8 +129,8 @@ static int mbm_run_test(const struct resctrl_test *test, const struct user_param
 		return ret;
 
 	ret = check_results(DEFAULT_SPAN);
-	if (ret && (get_vendor() == ARCH_INTEL))
-		ksft_print_msg("Intel MBM may be inaccurate when Sub-NUMA Clustering is enabled. Check BIOS configuration.\n");
+	if (ret && (get_vendor() == ARCH_INTEL) && !snc_kernel_support())
+		ksft_print_msg("Kernel doesn't support Sub-NUMA Clustering but it is enabled. Check BIOS configuration.\n");
 
 	return ret;
 }
diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h
index 3dd5d6779786..2bd7c3f71733 100644
--- a/tools/testing/selftests/resctrl/resctrl.h
+++ b/tools/testing/selftests/resctrl/resctrl.h
@@ -28,6 +28,7 @@
 #define RESCTRL_PATH		"/sys/fs/resctrl"
 #define PHYS_ID_PATH		"/sys/devices/system/cpu/cpu"
 #define INFO_PATH		"/sys/fs/resctrl/info"
+#define SIZE_PATH		"/sys/fs/resctrl/size"
 
 /*
  * CPU vendor IDs
@@ -165,12 +166,14 @@ unsigned long create_bit_mask(unsigned int start, unsigned int len);
 unsigned int count_contiguous_bits(unsigned long val, unsigned int *start);
 int get_full_cbm(const char *cache_type, unsigned long *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);
 int resource_info_unsigned_get(const char *resource, const char *filename, unsigned int *val);
+int get_sys_cache_size(int cpu_no, const char *cache_type, unsigned long *cache_size);
+int get_resctrl_cache_size(const char *cache_type, unsigned long *cache_size);
 void ctrlc_handler(int signum, siginfo_t *info, void *ptr);
 int signal_handler_register(const struct resctrl_test *test);
 void signal_handler_unregister(void);
 unsigned int count_bits(unsigned long n);
+int snc_kernel_support(void);
 
 void perf_event_attr_initialize(struct perf_event_attr *pea, __u64 config);
 void perf_event_initialize_read_format(struct perf_event_read *pe_read);
diff --git a/tools/testing/selftests/resctrl/resctrlfs.c b/tools/testing/selftests/resctrl/resctrlfs.c
index e4d3624a8817..88f97db72246 100644
--- a/tools/testing/selftests/resctrl/resctrlfs.c
+++ b/tools/testing/selftests/resctrl/resctrlfs.c
@@ -214,14 +214,14 @@ int snc_ways(void)
 }
 
 /*
- * get_cache_size - Get cache size for a specified CPU
+ * get_sys_cache_size - Get cache size for a specified CPU
  * @cpu_no:	CPU number
  * @cache_type:	Cache level L2/L3
  * @cache_size:	pointer to cache_size
  *
  * Return: = 0 on success, < 0 on failure.
  */
-int get_cache_size(int cpu_no, const char *cache_type, unsigned long *cache_size)
+int get_sys_cache_size(int cpu_no, const char *cache_type, unsigned long *cache_size)
 {
 	char cache_path[1024], cache_str[64];
 	int length, i, cache_num;
@@ -273,6 +273,44 @@ int get_cache_size(int cpu_no, const char *cache_type, unsigned long *cache_size
 	return 0;
 }
 
+/*
+ * get_resctrl_cache_size - Get cache size as reported by resctrl
+ * @cache_type:	Cache level L2/L3
+ * @cache_size:	pointer to cache_size
+ *
+ * Return: = 0 on success, < 0 on failure.
+ */
+int get_resctrl_cache_size(const char *cache_type, unsigned long *cache_size)
+{
+	char line[256], cache_prefix[16], *stripped_line, *token;
+	size_t len;
+	FILE *fp;
+
+	strcpy(cache_prefix, cache_type);
+	strncat(cache_prefix, ":", 1);
+
+	fp = fopen(SIZE_PATH, "r");
+	if (!fp) {
+		ksft_print_msg("Failed to open %s : '%s'\n",
+			       SIZE_PATH, strerror(errno));
+		return -1;
+	}
+
+	while (fgets(line, sizeof(line), fp)) {
+		stripped_line = strstr(line, cache_prefix);
+
+		if (stripped_line) {
+			len = strlen(cache_prefix);
+			stripped_line += len;
+			token = strtok(stripped_line, ";");
+			if (sscanf(token, "0=%lu", cache_size) <= 0)
+				return -1;
+		}
+	}
+	fclose(fp);
+	return 0;
+}
+
 #define CORE_SIBLINGS_PATH	"/sys/bus/cpu/devices/cpu"
 
 /*
@@ -935,3 +973,33 @@ unsigned int count_bits(unsigned long n)
 
 	return count;
 }
+
+/**
+ * snc_kernel_support - Compare system reported cache size and resctrl
+ * reported cache size to get an idea if SNC is supported on the kernel side.
+ *
+ * Return: 0 if not supported, 1 if SNC is disabled or SNC is both enabled and
+ * supported, < 0 on failure.
+ */
+int snc_kernel_support(void)
+{
+	unsigned long resctrl_cache_size, node_cache_size;
+	int ret;
+
+	/* If SNC is disabled then its kernel support isn't important. */
+	if (snc_ways() == 1)
+		return 1;
+
+	ret = get_sys_cache_size(0, "L3", &node_cache_size);
+	if (ret < 0)
+		return ret;
+
+	ret = get_resctrl_cache_size("L3", &resctrl_cache_size);
+	if (ret < 0)
+		return ret;
+
+	if (resctrl_cache_size == node_cache_size)
+		return 1;
+
+	return 0;
+}
-- 
2.45.0

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

[Luck, Tony]

If/when my SNC patches go upstream the SNC check could become:

snc_ways=$(ls -d /sys/fs/resctrl/mon_data/mon_L3_00/mon_sub_L3_* 2>/dev/null | wc -l)

assuming you have /sys/fs/resctrl mounted.

-Tony

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

[Maciej Wieczor-Retman]

On 2024-05-15 at 16:48:44 +0000, Luck, Tony wrote:
>If/when my SNC patches go upstream the SNC check could become:
>
>snc_ways=$(ls -d /sys/fs/resctrl/mon_data/mon_L3_00/mon_sub_L3_* 2>/dev/null | wc -l)

But this won't work without your kernel patches right? 

If they are already in the kernel used by the person launching the selftests
then there shouldn't be any problems to report. The idea was that if the
CMT/MBM/MBA selftests fail, the message with "SNC is the problem" is only
displayed if SNC is enabled and there is no kernel support for SNC.

>
>assuming you have /sys/fs/resctrl mounted.
>
>-Tony

-- 
Kind regards
Maciej Wieczór-Retman