[PATCH v4 0/4] selftests/resctrl: Add Hygon CPUs support and bug fixes

[PATCH v4 0/4] selftests/resctrl: Add Hygon CPUs support and bug fixes

[Xiaochen Shen]

The resctrl selftest currently exhibits several failures on Hygon CPUs
due to missing vendor detection and edge-case handling specific to
Hygon's architecture.

This patch series addresses three distinct issues:
1. A division-by-zero crash in SNC detection on some platforms (e.g.,
   Hygon).
2. Missing CPU vendor detection, causing the test to fail with
   "# Can not get vendor info..." on Hygon CPUs.
3. Incorrect handling of non-contiguous CBM support on Hygon CPUs.

These changes enable resctrl selftest to run successfully on
Hygon CPUs that support Platform QoS features.

Maintainer notes:
-----------------
Patch 1: selftests/resctrl: Fix a division by zero error on Hygon
 - This is a candidate for backport with "Fixes:" tag.

Patch 2: selftests/resctrl: Define CPU vendor IDs as bits to match usage
 - This is *not* a candidate for backport since it is an enhancement and
   preparatory patch for patch 3.

Patch 3: selftests/resctrl: Add CPU vendor detection for Hygon
Patch 4: selftests/resctrl: Fix non-contiguous CBM check for Hygon
 - Even though they are fixes they are *not* candidates for backport
   since they are based on another patch series (x86/resctrl: Fix
   Platform QoS issues for Hygon) which is in process of being added to
   resctrl.
-----------------

Changelog:
v4:
- Cover letter: add maintainer notes outlining how these patches to be
  handled (Reinette).
- Re-organize the patch series to move original patch 3 to the beginning
  of series. The patch order has changed between v3 and v4 (Reinette):
     v3    ->    v4
  patch #3 -> patch #1
  patch #1 -> patch #2
  patch #2 -> patch #3
  patch #4 -> patch #4
- Patch 2:
  1. Resolve a conflict against latest upstream kernel (Reinette).
  2. Fix a nit to maintain the reverse fir ordering of variables in
     detect_vendor() (Reinette).
- Patch 3: add Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
- Patch 4: move the maintainer note into the cover letter (Reinette).

v3:
- Patch 1:
  1. Update the return types of detect_vendor() and get_vendor() from
     'int' to 'unsigned int' to align with their usage as bitmask values
     and to prevent potentially risky type conversions (Fenghua).
  2. Split the code changes of "define CPU vendor IDs as bits to match
     usage" from original patch 1 into a separate patch (this patch,
     suggested by Fenghua and Reinette).
  3. Introduce the flag 'initialized' to simplify the get_vendor() ->
     detect_vendor() logic (Reinette).
- Patch 2 (original patch 1):
  1. Move the code changes of "define CPU vendor IDs as bits to match
     usage" into patch 1.
- Patch 3 (original patch 2): 
  1. Fix a nit of code comment for affected platforms (Fenghua).
  2. Add Reviewed-by: Fenghua Yu <fenghuay@nvidia.com>.
- Patch 4 (original patch 3): 
  1. Fix a nit to avoid calling get_vendor() twice (Fenghua).
  2. Add Reviewed-by: Fenghua Yu <fenghuay@nvidia.com>.

v2:
- Patch 1: switch all of the vendor id bitmasks to use BIT() (Reinette)
- Patch 2: add Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
- Patch 3: add Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
           add a maintainer note to highlight it is not a candidate for
	   backport (Reinette)

Xiaochen Shen (4):
  selftests/resctrl: Fix a division by zero error on Hygon
  selftests/resctrl: Define CPU vendor IDs as bits to match usage
  selftests/resctrl: Add CPU vendor detection for Hygon
  selftests/resctrl: Fix non-contiguous CBM check for Hygon

 tools/testing/selftests/resctrl/cat_test.c    |  6 ++--
 tools/testing/selftests/resctrl/resctrl.h     |  8 ++++--
 .../testing/selftests/resctrl/resctrl_tests.c | 28 +++++++++++++------
 tools/testing/selftests/resctrl/resctrlfs.c   | 10 +++++++
 4 files changed, 39 insertions(+), 13 deletions(-)

-- 
2.47.3

[PATCH v4 1/4] selftests/resctrl: Fix a division by zero error on Hygon

[Xiaochen Shen]

Commit

  a1cd99e700ec ("selftests/resctrl: Adjust effective L3 cache size with SNC enabled")

introduced the snc_nodes_per_l3_cache() function to detect the Intel
Sub-NUMA Clustering (SNC) feature by comparing #CPUs in node0 with #CPUs
sharing LLC with CPU0. The function was designed to return:
  (1) >1: SNC mode is enabled.
  (2)  1: SNC mode is not enabled or not supported.

However, on certain Hygon CPUs, #CPUs sharing LLC with CPU0 is actually
less than #CPUs in node0. This results in snc_nodes_per_l3_cache()
returning 0 (calculated as cache_cpus / node_cpus).

This leads to a division by zero error in get_cache_size():
  *cache_size /= snc_nodes_per_l3_cache();

Causing the resctrl selftest to fail with:
  "Floating point exception (core dumped)"

Fix the issue by ensuring snc_nodes_per_l3_cache() returns 1 when SNC
mode is not supported on the platform.

Fixes: a1cd99e700ec ("selftests/resctrl: Adjust effective L3 cache size with SNC enabled")
Signed-off-by: Xiaochen Shen <shenxiaochen@open-hieco.net>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Fenghua Yu <fenghuay@nvidia.com>
---
 tools/testing/selftests/resctrl/resctrlfs.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/tools/testing/selftests/resctrl/resctrlfs.c b/tools/testing/selftests/resctrl/resctrlfs.c
index 195f04c4d158..b9c1bfb6cc02 100644
--- a/tools/testing/selftests/resctrl/resctrlfs.c
+++ b/tools/testing/selftests/resctrl/resctrlfs.c
@@ -243,6 +243,16 @@ int snc_nodes_per_l3_cache(void)
 		}
 		snc_mode = cache_cpus / node_cpus;
 
+		/*
+		 * On some platforms (e.g. Hygon),
+		 * cache_cpus < node_cpus, the calculated snc_mode is 0.
+		 *
+		 * Set snc_mode = 1 to indicate that SNC mode is not
+		 * supported on the platform.
+		 */
+		if (!snc_mode)
+			snc_mode = 1;
+
 		if (snc_mode > 1)
 			ksft_print_msg("SNC-%d mode discovered.\n", snc_mode);
 	}
-- 
2.47.3

[PATCH v4 2/4] selftests/resctrl: Define CPU vendor IDs as bits to match usage

[Xiaochen Shen]

The CPU vendor IDs are required to be unique bits because they're used
for vendor_specific bitmask in the struct resctrl_test.
Consider for example their usage in test_vendor_specific_check():
	return get_vendor() & test->vendor_specific

However, the definitions of CPU vendor IDs in file resctrl.h is quite
subtle as a bitmask value:
  #define ARCH_INTEL     1
  #define ARCH_AMD       2

A clearer and more maintainable approach is to define these CPU vendor
IDs using BIT(). This ensures each vendor corresponds to a distinct bit
and makes it obvious when adding new vendor IDs.

Accordingly, update the return types of detect_vendor() and get_vendor()
from 'int' to 'unsigned int' to align with their usage as bitmask values
and to prevent potentially risky type conversions.

Furthermore, introduce a bool flag 'initialized' to simplify the
get_vendor() -> detect_vendor() logic. This ensures the vendor ID is
detected only once and resolves the ambiguity of using the same variable
'vendor' both as a value and as a state.

Suggested-by: Reinette Chatre <reinette.chatre@intel.com>
Suggested-by: Fenghua Yu <fenghuay@nvidia.com>
Signed-off-by: Xiaochen Shen <shenxiaochen@open-hieco.net>
---
 tools/testing/selftests/resctrl/resctrl.h     |  7 ++---
 .../testing/selftests/resctrl/resctrl_tests.c | 26 +++++++++++++------
 2 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h
index 3c51bdac2dfa..4f9c7d04c98d 100644
--- a/tools/testing/selftests/resctrl/resctrl.h
+++ b/tools/testing/selftests/resctrl/resctrl.h
@@ -23,6 +23,7 @@
 #include <asm/unistd.h>
 #include <linux/perf_event.h>
 #include <linux/compiler.h>
+#include <linux/bits.h>
 #include "kselftest.h"
 
 #define MB			(1024 * 1024)
@@ -36,8 +37,8 @@
  * Define as bits because they're used for vendor_specific bitmask in
  * the struct resctrl_test.
  */
-#define ARCH_INTEL     1
-#define ARCH_AMD       2
+#define ARCH_INTEL	BIT(0)
+#define ARCH_AMD	BIT(1)
 
 #define END_OF_TESTS	1
 
@@ -163,7 +164,7 @@ extern int snc_unreliable;
 extern char llc_occup_path[1024];
 
 int snc_nodes_per_l3_cache(void);
-int get_vendor(void);
+unsigned int get_vendor(void);
 bool check_resctrlfs_support(void);
 int filter_dmesg(void);
 int get_domain_id(const char *resource, int cpu_no, int *domain_id);
diff --git a/tools/testing/selftests/resctrl/resctrl_tests.c b/tools/testing/selftests/resctrl/resctrl_tests.c
index 5154ffd821c4..980ecf2bcf10 100644
--- a/tools/testing/selftests/resctrl/resctrl_tests.c
+++ b/tools/testing/selftests/resctrl/resctrl_tests.c
@@ -23,16 +23,24 @@ static struct resctrl_test *resctrl_tests[] = {
 	&l2_noncont_cat_test,
 };
 
-static int detect_vendor(void)
+static unsigned int detect_vendor(void)
 {
-	FILE *inf = fopen("/proc/cpuinfo", "r");
-	int vendor_id = 0;
+	FILE *inf;
+	static unsigned int vendor_id;
 	char *s = NULL;
 	char *res;
+	static bool initialized;
 
-	if (!inf)
+	if (initialized)
 		return vendor_id;
 
+	inf = fopen("/proc/cpuinfo", "r");
+	if (!inf) {
+		vendor_id = 0;
+		initialized = true;
+		return vendor_id;
+	}
+
 	res = fgrep(inf, "vendor_id");
 
 	if (res)
@@ -45,15 +53,17 @@ static int detect_vendor(void)
 
 	fclose(inf);
 	free(res);
+
+	initialized = true;
 	return vendor_id;
 }
 
-int get_vendor(void)
+unsigned int get_vendor(void)
 {
-	static int vendor = -1;
+	unsigned int vendor;
+
+	vendor = detect_vendor();
 
-	if (vendor == -1)
-		vendor = detect_vendor();
 	if (vendor == 0)
 		ksft_print_msg("Can not get vendor info...\n");
 
-- 
2.47.3

Re: [PATCH v4 2/4] selftests/resctrl: Define CPU vendor IDs as bits to match usage

[Reinette Chatre]

Hi Xiaochen,

On 12/12/25 11:38 PM, Xiaochen Shen wrote:
> diff --git a/tools/testing/selftests/resctrl/resctrl_tests.c b/tools/testing/selftests/resctrl/resctrl_tests.c
> index 5154ffd821c4..980ecf2bcf10 100644
> --- a/tools/testing/selftests/resctrl/resctrl_tests.c
> +++ b/tools/testing/selftests/resctrl/resctrl_tests.c
> @@ -23,16 +23,24 @@ static struct resctrl_test *resctrl_tests[] = {
>  	&l2_noncont_cat_test,
>  };
>  
> -static int detect_vendor(void)
> +static unsigned int detect_vendor(void)
>  {
> -	FILE *inf = fopen("/proc/cpuinfo", "r");
> -	int vendor_id = 0;
> +	FILE *inf;
> +	static unsigned int vendor_id;
>  	char *s = NULL;
>  	char *res;
> +	static bool initialized;
>  

The changelog incorrectly claims that this should now match reverse fir ordering.
To be "reverse fir" ordered the declarations should look like:

	static unsigned int vendor_id;                                          
	static bool initialized;                                                
	char *s = NULL;                                                         
	FILE *inf;                                                              
	char *res;             


With this fixed:
| Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>

Reinette

Re: [PATCH v4 2/4] selftests/resctrl: Define CPU vendor IDs as bits to match usage

[Xiaochen Shen]

Hi Reinette,

On 12/17/2025 7:26 AM, Reinette Chatre wrote:
>> -static int detect_vendor(void)
>> +static unsigned int detect_vendor(void)
>>  {
>> -	FILE *inf = fopen("/proc/cpuinfo", "r");
>> -	int vendor_id = 0;
>> +	FILE *inf;
>> +	static unsigned int vendor_id;
>>  	char *s = NULL;
>>  	char *res;
>> +	static bool initialized;
>>  
> The changelog incorrectly claims that this should now match reverse fir ordering.
> To be "reverse fir" ordered the declarations should look like:
> 
> 	static unsigned int vendor_id;                                          
> 	static bool initialized;                                                
> 	char *s = NULL;                                                         
> 	FILE *inf;                                                              
> 	char *res;             

Thank you! I will fix it on v5 patch.


> 
> 
> With this fixed:
> | Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>

Thank you!


Best regards,
Xiaochen Shen

[PATCH v4 3/4] selftests/resctrl: Add CPU vendor detection for Hygon

[Xiaochen Shen]

The resctrl selftest currently fails on Hygon CPUs that support Platform
QoS features, printing the error:

  "# Can not get vendor info..."

This occurs because vendor detection is missing for Hygon CPUs.

Fix this by extending the CPU vendor detection logic to include
Hygon's vendor ID.

Signed-off-by: Xiaochen Shen <shenxiaochen@open-hieco.net>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
---
 tools/testing/selftests/resctrl/resctrl.h       | 1 +
 tools/testing/selftests/resctrl/resctrl_tests.c | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h
index 4f9c7d04c98d..afe635b6e48d 100644
--- a/tools/testing/selftests/resctrl/resctrl.h
+++ b/tools/testing/selftests/resctrl/resctrl.h
@@ -39,6 +39,7 @@
  */
 #define ARCH_INTEL	BIT(0)
 #define ARCH_AMD	BIT(1)
+#define ARCH_HYGON	BIT(2)
 
 #define END_OF_TESTS	1
 
diff --git a/tools/testing/selftests/resctrl/resctrl_tests.c b/tools/testing/selftests/resctrl/resctrl_tests.c
index 980ecf2bcf10..78626bbae976 100644
--- a/tools/testing/selftests/resctrl/resctrl_tests.c
+++ b/tools/testing/selftests/resctrl/resctrl_tests.c
@@ -50,6 +50,8 @@ static unsigned int detect_vendor(void)
 		vendor_id = ARCH_INTEL;
 	else if (s && !strcmp(s, ": AuthenticAMD\n"))
 		vendor_id = ARCH_AMD;
+	else if (s && !strcmp(s, ": HygonGenuine\n"))
+		vendor_id = ARCH_HYGON;
 
 	fclose(inf);
 	free(res);
-- 
2.47.3

[PATCH v4 4/4] selftests/resctrl: Fix non-contiguous CBM check for Hygon

[Xiaochen Shen]

The resctrl selftest currently fails on Hygon CPUs that always supports
non-contiguous CBM, printing the error:

  "# Hardware and kernel differ on non-contiguous CBM support!"

This occurs because the arch_supports_noncont_cat() function lacks
vendor detection for Hygon CPUs, preventing proper identification of
their non-contiguous CBM capability.

Fix this by adding Hygon vendor ID detection to
arch_supports_noncont_cat().

Signed-off-by: Xiaochen Shen <shenxiaochen@open-hieco.net>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Fenghua Yu <fenghuay@nvidia.com>
---
 tools/testing/selftests/resctrl/cat_test.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/resctrl/cat_test.c b/tools/testing/selftests/resctrl/cat_test.c
index 94cfdba5308d..f00b622c1460 100644
--- a/tools/testing/selftests/resctrl/cat_test.c
+++ b/tools/testing/selftests/resctrl/cat_test.c
@@ -290,8 +290,10 @@ static int cat_run_test(const struct resctrl_test *test, const struct user_param
 
 static bool arch_supports_noncont_cat(const struct resctrl_test *test)
 {
-	/* AMD always supports non-contiguous CBM. */
-	if (get_vendor() == ARCH_AMD)
+	unsigned int vendor_id = get_vendor();
+
+	/* AMD and Hygon always support non-contiguous CBM. */
+	if (vendor_id == ARCH_AMD || vendor_id == ARCH_HYGON)
 		return true;
 
 #if defined(__i386__) || defined(__x86_64__) /* arch */
-- 
2.47.3