[PATCH v2 0/7] Update DSCR tests

[PATCH v2 0/7] Update DSCR tests

[Benjamin Gray]

The randomness based DSCR tests currently have a low probability of doing
any writes to the DSCR, making them inefficient in uncovering bugs.

This series adds lockstep variants to these RNG tests, to ensure the happy
path is always tested, and improves the randomness and size of the RNG
tests.

It also removes many iterations of the sysfs DSCR test, allowing the default
timeout to be re-enabled.

v2:	* Pull bind_to_cpu() out to utils.c and allow an automatically
	  determined CPU selection.

Previous versions:
v1: https://lore.kernel.org/all/20230307005515.174362-1-bgray@linux.ibm.com/

Benjamin Gray (7):
  selftests/powerpc/dscr: Correct typos
  selftests/powerpc: Move bind_to_cpu() to utils.h
  selftests/powerpc: Allow bind_to_cpu() to automatically pick CPU
  selftests/powerpc/dscr: Add lockstep test cases to DSCR explicit tests
  selftests/powerpc/dscr: Improve DSCR explicit random test case
  selftests/powerpc/dscr: Speed up DSCR sysfs tests
  selftests/powerpc/dscr: Restore timeout to DSCR selftests

 tools/testing/selftests/powerpc/dscr/Makefile |   3 +-
 tools/testing/selftests/powerpc/dscr/dscr.h   |   4 -
 .../powerpc/dscr/dscr_default_test.c          | 207 +++++++++++-------
 .../powerpc/dscr/dscr_explicit_test.c         | 169 +++++++++++---
 .../powerpc/dscr/dscr_inherit_test.c          |   4 +-
 .../selftests/powerpc/dscr/dscr_sysfs_test.c  |  11 +-
 .../selftests/powerpc/dscr/dscr_user_test.c   |   4 +-
 tools/testing/selftests/powerpc/dscr/settings |   1 -
 .../testing/selftests/powerpc/include/utils.h |   3 +
 .../pmu/ebb/cpu_event_pinned_vs_ebb_test.c    |   3 +-
 .../powerpc/pmu/ebb/cpu_event_vs_ebb_test.c   |   3 +-
 .../powerpc/pmu/ebb/ebb_vs_cpu_event_test.c   |   3 +-
 .../powerpc/pmu/ebb/multi_ebb_procs_test.c    |   6 +-
 tools/testing/selftests/powerpc/pmu/lib.c     |  19 +-
 tools/testing/selftests/powerpc/pmu/lib.h     |   1 -
 tools/testing/selftests/powerpc/utils.c       |  23 ++
 16 files changed, 303 insertions(+), 161 deletions(-)
 delete mode 100644 tools/testing/selftests/powerpc/dscr/settings

--
2.39.2

[PATCH v2 1/7] selftests/powerpc/dscr: Correct typos

[Benjamin Gray]

Correct a couple of typos while working on other improvements to the
DSCR tests.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
---
 tools/testing/selftests/powerpc/dscr/dscr_explicit_test.c | 4 ++--
 tools/testing/selftests/powerpc/dscr/dscr_inherit_test.c  | 4 ++--
 tools/testing/selftests/powerpc/dscr/dscr_user_test.c     | 4 ++--
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/powerpc/dscr/dscr_explicit_test.c b/tools/testing/selftests/powerpc/dscr/dscr_explicit_test.c
index 32fcf2b324b1..5659d98cf340 100644
--- a/tools/testing/selftests/powerpc/dscr/dscr_explicit_test.c
+++ b/tools/testing/selftests/powerpc/dscr/dscr_explicit_test.c
@@ -7,8 +7,8 @@
  * privilege state SPR and the problem state SPR for this purpose.
  *
  * When using the privilege state SPR, the instructions such as
- * mfspr or mtspr are priviledged and the kernel emulates them
- * for us. Instructions using problem state SPR can be exuecuted
+ * mfspr or mtspr are privileged and the kernel emulates them
+ * for us. Instructions using problem state SPR can be executed
  * directly without any emulation if the HW supports them. Else
  * they also get emulated by the kernel.
  *
diff --git a/tools/testing/selftests/powerpc/dscr/dscr_inherit_test.c b/tools/testing/selftests/powerpc/dscr/dscr_inherit_test.c
index f9dfd3d3c2d5..68ce328e813e 100644
--- a/tools/testing/selftests/powerpc/dscr/dscr_inherit_test.c
+++ b/tools/testing/selftests/powerpc/dscr/dscr_inherit_test.c
@@ -7,8 +7,8 @@
  * value using mfspr.
  *
  * When using the privilege state SPR, the instructions such as
- * mfspr or mtspr are priviledged and the kernel emulates them
- * for us. Instructions using problem state SPR can be exuecuted
+ * mfspr or mtspr are privileged and the kernel emulates them
+ * for us. Instructions using problem state SPR can be executed
  * directly without any emulation if the HW supports them. Else
  * they also get emulated by the kernel.
  *
diff --git a/tools/testing/selftests/powerpc/dscr/dscr_user_test.c b/tools/testing/selftests/powerpc/dscr/dscr_user_test.c
index e09072446dd3..67bb872a246a 100644
--- a/tools/testing/selftests/powerpc/dscr/dscr_user_test.c
+++ b/tools/testing/selftests/powerpc/dscr/dscr_user_test.c
@@ -8,8 +8,8 @@
  * numbers.
  *
  * When using the privilege state SPR, the instructions such as
- * mfspr or mtspr are priviledged and the kernel emulates them
- * for us. Instructions using problem state SPR can be exuecuted
+ * mfspr or mtspr are privileged and the kernel emulates them
+ * for us. Instructions using problem state SPR can be executed
  * directly without any emulation if the HW supports them. Else
  * they also get emulated by the kernel.
  *
-- 
2.39.2

[PATCH v2 2/7] selftests/powerpc: Move bind_to_cpu() to utils.h

[Benjamin Gray]

This function will be useful in the DSCR test patches later in this
series, so promote it to be shared by all powerpc selftests.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>

---

v2:	* New in v2
---
 tools/testing/selftests/powerpc/include/utils.h |  1 +
 tools/testing/selftests/powerpc/pmu/lib.c       | 13 -------------
 tools/testing/selftests/powerpc/pmu/lib.h       |  1 -
 tools/testing/selftests/powerpc/utils.c         | 12 ++++++++++++
 4 files changed, 13 insertions(+), 14 deletions(-)

diff --git a/tools/testing/selftests/powerpc/include/utils.h b/tools/testing/selftests/powerpc/include/utils.h
index eed7dd7582b2..d3589e16a20f 100644
--- a/tools/testing/selftests/powerpc/include/utils.h
+++ b/tools/testing/selftests/powerpc/include/utils.h
@@ -32,6 +32,7 @@ void *find_auxv_entry(int type, char *auxv);
 void *get_auxv_entry(int type);
 
 int pick_online_cpu(void);
+int bind_to_cpu(int cpu);
 
 int parse_intmax(const char *buffer, size_t count, intmax_t *result, int base);
 int parse_uintmax(const char *buffer, size_t count, uintmax_t *result, int base);
diff --git a/tools/testing/selftests/powerpc/pmu/lib.c b/tools/testing/selftests/powerpc/pmu/lib.c
index 719f94f10d41..144f90a78d69 100644
--- a/tools/testing/selftests/powerpc/pmu/lib.c
+++ b/tools/testing/selftests/powerpc/pmu/lib.c
@@ -14,19 +14,6 @@
 #include "utils.h"
 #include "lib.h"
 
-
-int bind_to_cpu(int cpu)
-{
-	cpu_set_t mask;
-
-	printf("Binding to cpu %d\n", cpu);
-
-	CPU_ZERO(&mask);
-	CPU_SET(cpu, &mask);
-
-	return sched_setaffinity(0, sizeof(mask), &mask);
-}
-
 #define PARENT_TOKEN	0xAA
 #define CHILD_TOKEN	0x55
 
diff --git a/tools/testing/selftests/powerpc/pmu/lib.h b/tools/testing/selftests/powerpc/pmu/lib.h
index bf1bec013bbb..1d62403ae6ea 100644
--- a/tools/testing/selftests/powerpc/pmu/lib.h
+++ b/tools/testing/selftests/powerpc/pmu/lib.h
@@ -20,7 +20,6 @@ union pipe {
 	int fds[2];
 };
 
-extern int bind_to_cpu(int cpu);
 extern int kill_child_and_wait(pid_t child_pid);
 extern int wait_for_child(pid_t child_pid);
 extern int sync_with_child(union pipe read_pipe, union pipe write_pipe);
diff --git a/tools/testing/selftests/powerpc/utils.c b/tools/testing/selftests/powerpc/utils.c
index 7c8cfedb012a..cdb996dba703 100644
--- a/tools/testing/selftests/powerpc/utils.c
+++ b/tools/testing/selftests/powerpc/utils.c
@@ -452,6 +452,18 @@ int pick_online_cpu(void)
 	return cpu;
 }
 
+int bind_to_cpu(int cpu)
+{
+	cpu_set_t mask;
+
+	printf("Binding to cpu %d\n", cpu);
+
+	CPU_ZERO(&mask);
+	CPU_SET(cpu, &mask);
+
+	return sched_setaffinity(0, sizeof(mask), &mask);
+}
+
 bool is_ppc64le(void)
 {
 	struct utsname uts;
-- 
2.39.2

[PATCH v2 3/7] selftests/powerpc: Allow bind_to_cpu() to automatically pick CPU

[Benjamin Gray]

All current users of bind_to_cpu() don't care _which_ CPU they get, just
that they are bound to a single free one. So alter the interface to

	1. Accept a BIND_CPU_ANY value that tells it to automatically
	   pick a CPU
	2. Return the picked CPU

And convert all these users to bind_to_cpu(BIND_CPU_ANY).

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>

---

v2:	* New in v2
---
 tools/testing/selftests/powerpc/include/utils.h     |  2 ++
 .../powerpc/pmu/ebb/cpu_event_pinned_vs_ebb_test.c  |  3 +--
 .../powerpc/pmu/ebb/cpu_event_vs_ebb_test.c         |  3 +--
 .../powerpc/pmu/ebb/ebb_vs_cpu_event_test.c         |  3 +--
 .../powerpc/pmu/ebb/multi_ebb_procs_test.c          |  6 ++----
 tools/testing/selftests/powerpc/pmu/lib.c           |  6 ++----
 tools/testing/selftests/powerpc/utils.c             | 13 ++++++++++++-
 7 files changed, 21 insertions(+), 15 deletions(-)

diff --git a/tools/testing/selftests/powerpc/include/utils.h b/tools/testing/selftests/powerpc/include/utils.h
index d3589e16a20f..44bfd48b93d6 100644
--- a/tools/testing/selftests/powerpc/include/utils.h
+++ b/tools/testing/selftests/powerpc/include/utils.h
@@ -31,6 +31,8 @@ int read_auxv(char *buf, ssize_t buf_size);
 void *find_auxv_entry(int type, char *auxv);
 void *get_auxv_entry(int type);
 
+#define BIND_CPU_ANY	(-1)
+
 int pick_online_cpu(void);
 int bind_to_cpu(int cpu);
 
diff --git a/tools/testing/selftests/powerpc/pmu/ebb/cpu_event_pinned_vs_ebb_test.c b/tools/testing/selftests/powerpc/pmu/ebb/cpu_event_pinned_vs_ebb_test.c
index 3cd33eb51e5e..fab7f34d7ce1 100644
--- a/tools/testing/selftests/powerpc/pmu/ebb/cpu_event_pinned_vs_ebb_test.c
+++ b/tools/testing/selftests/powerpc/pmu/ebb/cpu_event_pinned_vs_ebb_test.c
@@ -45,9 +45,8 @@ int cpu_event_pinned_vs_ebb(void)
 
 	SKIP_IF(!ebb_is_supported());
 
-	cpu = pick_online_cpu();
+	cpu = bind_to_cpu(BIND_CPU_ANY);
 	FAIL_IF(cpu < 0);
-	FAIL_IF(bind_to_cpu(cpu));
 
 	FAIL_IF(pipe(read_pipe.fds) == -1);
 	FAIL_IF(pipe(write_pipe.fds) == -1);
diff --git a/tools/testing/selftests/powerpc/pmu/ebb/cpu_event_vs_ebb_test.c b/tools/testing/selftests/powerpc/pmu/ebb/cpu_event_vs_ebb_test.c
index 8466ef9d7de8..7c54c262036e 100644
--- a/tools/testing/selftests/powerpc/pmu/ebb/cpu_event_vs_ebb_test.c
+++ b/tools/testing/selftests/powerpc/pmu/ebb/cpu_event_vs_ebb_test.c
@@ -43,9 +43,8 @@ int cpu_event_vs_ebb(void)
 
 	SKIP_IF(!ebb_is_supported());
 
-	cpu = pick_online_cpu();
+	cpu = bind_to_cpu(BIND_CPU_ANY);
 	FAIL_IF(cpu < 0);
-	FAIL_IF(bind_to_cpu(cpu));
 
 	FAIL_IF(pipe(read_pipe.fds) == -1);
 	FAIL_IF(pipe(write_pipe.fds) == -1);
diff --git a/tools/testing/selftests/powerpc/pmu/ebb/ebb_vs_cpu_event_test.c b/tools/testing/selftests/powerpc/pmu/ebb/ebb_vs_cpu_event_test.c
index 4d822cb3589c..d7064b54c64f 100644
--- a/tools/testing/selftests/powerpc/pmu/ebb/ebb_vs_cpu_event_test.c
+++ b/tools/testing/selftests/powerpc/pmu/ebb/ebb_vs_cpu_event_test.c
@@ -43,9 +43,8 @@ int ebb_vs_cpu_event(void)
 
 	SKIP_IF(!ebb_is_supported());
 
-	cpu = pick_online_cpu();
+	cpu = bind_to_cpu(BIND_CPU_ANY);
 	FAIL_IF(cpu < 0);
-	FAIL_IF(bind_to_cpu(cpu));
 
 	FAIL_IF(pipe(read_pipe.fds) == -1);
 	FAIL_IF(pipe(write_pipe.fds) == -1);
diff --git a/tools/testing/selftests/powerpc/pmu/ebb/multi_ebb_procs_test.c b/tools/testing/selftests/powerpc/pmu/ebb/multi_ebb_procs_test.c
index 9b0f70d59702..4ac22b2e774f 100644
--- a/tools/testing/selftests/powerpc/pmu/ebb/multi_ebb_procs_test.c
+++ b/tools/testing/selftests/powerpc/pmu/ebb/multi_ebb_procs_test.c
@@ -75,13 +75,11 @@ static int cycles_child(void)
 int multi_ebb_procs(void)
 {
 	pid_t pids[NR_CHILDREN];
-	int cpu, rc, i;
+	int rc, i;
 
 	SKIP_IF(!ebb_is_supported());
 
-	cpu = pick_online_cpu();
-	FAIL_IF(cpu < 0);
-	FAIL_IF(bind_to_cpu(cpu));
+	FAIL_IF(bind_to_cpu(BIND_CPU_ANY) < 0);
 
 	for (i = 0; i < NR_CHILDREN; i++) {
 		pids[i] = fork();
diff --git a/tools/testing/selftests/powerpc/pmu/lib.c b/tools/testing/selftests/powerpc/pmu/lib.c
index 144f90a78d69..321357987408 100644
--- a/tools/testing/selftests/powerpc/pmu/lib.c
+++ b/tools/testing/selftests/powerpc/pmu/lib.c
@@ -103,12 +103,10 @@ static int eat_cpu_child(union pipe read_pipe, union pipe write_pipe)
 pid_t eat_cpu(int (test_function)(void))
 {
 	union pipe read_pipe, write_pipe;
-	int cpu, rc;
+	int rc;
 	pid_t pid;
 
-	cpu = pick_online_cpu();
-	FAIL_IF(cpu < 0);
-	FAIL_IF(bind_to_cpu(cpu));
+	FAIL_IF(bind_to_cpu(BIND_CPU_ANY) < 0);
 
 	if (pipe(read_pipe.fds) == -1)
 		return -1;
diff --git a/tools/testing/selftests/powerpc/utils.c b/tools/testing/selftests/powerpc/utils.c
index cdb996dba703..252fb4a95e90 100644
--- a/tools/testing/selftests/powerpc/utils.c
+++ b/tools/testing/selftests/powerpc/utils.c
@@ -455,13 +455,24 @@ int pick_online_cpu(void)
 int bind_to_cpu(int cpu)
 {
 	cpu_set_t mask;
+	int err;
+
+	if (cpu == BIND_CPU_ANY) {
+		cpu = pick_online_cpu();
+		if (cpu < 0)
+			return cpu;
+	}
 
 	printf("Binding to cpu %d\n", cpu);
 
 	CPU_ZERO(&mask);
 	CPU_SET(cpu, &mask);
 
-	return sched_setaffinity(0, sizeof(mask), &mask);
+	err = sched_setaffinity(0, sizeof(mask), &mask);
+	if (err)
+		return err;
+
+	return cpu;
 }
 
 bool is_ppc64le(void)
-- 
2.39.2

[PATCH v2 4/7] selftests/powerpc/dscr: Add lockstep test cases to DSCR explicit tests

[Benjamin Gray]

Add new cases to the relevant tests that use explicitly synchronized
threads to test the behaviour across context switches with less
randomness. By locking the participants to the same CPU we guarantee a
context switch occurs each time they make progress, which is a likely
failure point if the kernel is not tracking the thread local DSCR
correctly.

The random case is left in to keep exercising potential edge cases.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>

---

v2:	* Use the bind_to_cpu() added in the previous 2 new patches
	  instead of reimplementing it
---
 tools/testing/selftests/powerpc/dscr/Makefile |  1 +
 .../powerpc/dscr/dscr_default_test.c          | 87 ++++++++++++++++---
 .../powerpc/dscr/dscr_explicit_test.c         | 85 +++++++++++++++++-
 3 files changed, 159 insertions(+), 14 deletions(-)

diff --git a/tools/testing/selftests/powerpc/dscr/Makefile b/tools/testing/selftests/powerpc/dscr/Makefile
index 845db6273a1b..b29a8863a734 100644
--- a/tools/testing/selftests/powerpc/dscr/Makefile
+++ b/tools/testing/selftests/powerpc/dscr/Makefile
@@ -9,5 +9,6 @@ top_srcdir = ../../../../..
 include ../../lib.mk
 
 $(OUTPUT)/dscr_default_test: LDLIBS += -lpthread
+$(OUTPUT)/dscr_explicit_test: LDLIBS += -lpthread
 
 $(TEST_GEN_PROGS): ../harness.c ../utils.c
diff --git a/tools/testing/selftests/powerpc/dscr/dscr_default_test.c b/tools/testing/selftests/powerpc/dscr/dscr_default_test.c
index e76611e608af..18e533d46c9a 100644
--- a/tools/testing/selftests/powerpc/dscr/dscr_default_test.c
+++ b/tools/testing/selftests/powerpc/dscr/dscr_default_test.c
@@ -9,8 +9,66 @@
  * Copyright 2012, Anton Blanchard, IBM Corporation.
  * Copyright 2015, Anshuman Khandual, IBM Corporation.
  */
+
+#define _GNU_SOURCE
+
 #include "dscr.h"
 
+#include <pthread.h>
+#include <semaphore.h>
+#include <unistd.h>
+
+static void *dscr_default_lockstep_writer(void *arg)
+{
+	sem_t *reader_sem = (sem_t *)arg;
+	sem_t *writer_sem = (sem_t *)arg + 1;
+	unsigned long expected_dscr = 0;
+
+	for (int i = 0; i < COUNT; i++) {
+		FAIL_IF_EXIT(sem_wait(writer_sem));
+
+		set_default_dscr(expected_dscr);
+		expected_dscr = (expected_dscr + 1) % DSCR_MAX;
+
+		FAIL_IF_EXIT(sem_post(reader_sem));
+	}
+
+	return NULL;
+}
+
+int dscr_default_lockstep_test(void)
+{
+	pthread_t writer;
+	sem_t rw_semaphores[2];
+	sem_t *reader_sem = &rw_semaphores[0];
+	sem_t *writer_sem = &rw_semaphores[1];
+	unsigned long expected_dscr = 0;
+
+	SKIP_IF(!have_hwcap2(PPC_FEATURE2_DSCR));
+
+	FAIL_IF(sem_init(reader_sem, 0, 0));
+	FAIL_IF(sem_init(writer_sem, 0, 1));  /* writer starts first */
+	FAIL_IF(bind_to_cpu(BIND_CPU_ANY) < 0);
+	FAIL_IF(pthread_create(&writer, NULL, dscr_default_lockstep_writer, (void *)rw_semaphores));
+
+	for (int i = 0; i < COUNT ; i++) {
+		FAIL_IF(sem_wait(reader_sem));
+
+		FAIL_IF(get_dscr() != expected_dscr);
+		FAIL_IF(get_dscr_usr() != expected_dscr);
+
+		expected_dscr = (expected_dscr + 1) % DSCR_MAX;
+
+		FAIL_IF(sem_post(writer_sem));
+	}
+
+	FAIL_IF(pthread_join(writer, NULL));
+	FAIL_IF(sem_destroy(reader_sem));
+	FAIL_IF(sem_destroy(writer_sem));
+
+	return 0;
+}
+
 static unsigned long dscr;		/* System DSCR default */
 static unsigned long sequence;
 static unsigned long result[THREADS];
@@ -57,16 +115,13 @@ static void *do_test(void *in)
 	pthread_exit(&result[thread]);
 }
 
-int dscr_default(void)
+int dscr_default_random_test(void)
 {
 	pthread_t threads[THREADS];
 	unsigned long i, *status[THREADS];
-	unsigned long orig_dscr_default;
 
 	SKIP_IF(!have_hwcap2(PPC_FEATURE2_DSCR));
 
-	orig_dscr_default = get_default_dscr();
-
 	/* Initial DSCR default */
 	dscr = 1;
 	set_default_dscr(dscr);
@@ -75,7 +130,7 @@ int dscr_default(void)
 	for (i = 0; i < THREADS; i++) {
 		if (pthread_create(&threads[i], NULL, do_test, (void *)i)) {
 			perror("pthread_create() failed");
-			goto fail;
+			return 1;
 		}
 	}
 
@@ -104,23 +159,31 @@ int dscr_default(void)
 	for (i = 0; i < THREADS; i++) {
 		if (pthread_join(threads[i], (void **)&(status[i]))) {
 			perror("pthread_join() failed");
-			goto fail;
+			return 1;
 		}
 
 		if (*status[i]) {
 			printf("%ldth thread failed to join with %ld status\n",
 								i, *status[i]);
-			goto fail;
+			return 1;
 		}
 	}
-	set_default_dscr(orig_dscr_default);
 	return 0;
-fail:
-	set_default_dscr(orig_dscr_default);
-	return 1;
 }
 
 int main(int argc, char *argv[])
 {
-	return test_harness(dscr_default, "dscr_default_test");
+	unsigned long orig_dscr_default = 0;
+	int err = 0;
+
+	if (have_hwcap2(PPC_FEATURE2_DSCR))
+		orig_dscr_default = get_default_dscr();
+
+	err |= test_harness(dscr_default_lockstep_test, "dscr_default_lockstep_test");
+	err |= test_harness(dscr_default_random_test, "dscr_default_random_test");
+
+	if (have_hwcap2(PPC_FEATURE2_DSCR))
+		set_default_dscr(orig_dscr_default);
+
+	return err;
 }
diff --git a/tools/testing/selftests/powerpc/dscr/dscr_explicit_test.c b/tools/testing/selftests/powerpc/dscr/dscr_explicit_test.c
index 5659d98cf340..3b98b9a88207 100644
--- a/tools/testing/selftests/powerpc/dscr/dscr_explicit_test.c
+++ b/tools/testing/selftests/powerpc/dscr/dscr_explicit_test.c
@@ -15,9 +15,78 @@
  * Copyright 2012, Anton Blanchard, IBM Corporation.
  * Copyright 2015, Anshuman Khandual, IBM Corporation.
  */
+
+#define _GNU_SOURCE
+
 #include "dscr.h"
+#include "utils.h"
+
+#include <pthread.h>
+#include <sched.h>
+#include <semaphore.h>
+
+void *dscr_explicit_lockstep_thread(void *args)
+{
+	sem_t *prev = (sem_t *)args;
+	sem_t *next = (sem_t *)args + 1;
+	unsigned long expected_dscr = 0;
+
+	set_dscr(expected_dscr);
+	srand(gettid());
+
+	for (int i = 0; i < COUNT; i++) {
+		FAIL_IF_EXIT(sem_wait(prev));
+
+		FAIL_IF_EXIT(expected_dscr != get_dscr());
+		FAIL_IF_EXIT(expected_dscr != get_dscr_usr());
+
+		expected_dscr = (expected_dscr + 1) % DSCR_MAX;
+		set_dscr(expected_dscr);
+
+		FAIL_IF_EXIT(sem_post(next));
+	}
+
+	return NULL;
+}
+
+int dscr_explicit_lockstep_test(void)
+{
+	pthread_t thread;
+	sem_t semaphores[2];
+	sem_t *prev = &semaphores[1];  /* reversed prev/next than for the other thread */
+	sem_t *next = &semaphores[0];
+	unsigned long expected_dscr = 0;
+
+	SKIP_IF(!have_hwcap2(PPC_FEATURE2_DSCR));
+
+	srand(gettid());
+	set_dscr(expected_dscr);
+
+	FAIL_IF(sem_init(prev, 0, 0));
+	FAIL_IF(sem_init(next, 0, 1));  /* other thread starts first */
+	FAIL_IF(bind_to_cpu(BIND_CPU_ANY) < 0);
+	FAIL_IF(pthread_create(&thread, NULL, dscr_explicit_lockstep_thread, (void *)semaphores));
+
+	for (int i = 0; i < COUNT; i++) {
+		FAIL_IF(sem_wait(prev));
+
+		FAIL_IF(expected_dscr != get_dscr());
+		FAIL_IF(expected_dscr != get_dscr_usr());
+
+		expected_dscr = (expected_dscr - 1) % DSCR_MAX;
+		set_dscr(expected_dscr);
+
+		FAIL_IF(sem_post(next));
+	}
 
-int dscr_explicit(void)
+	FAIL_IF(pthread_join(thread, NULL));
+	FAIL_IF(sem_destroy(prev));
+	FAIL_IF(sem_destroy(next));
+
+	return 0;
+}
+
+int dscr_explicit_random_test(void)
 {
 	unsigned long i, dscr = 0;
 
@@ -66,5 +135,17 @@ int dscr_explicit(void)
 
 int main(int argc, char *argv[])
 {
-	return test_harness(dscr_explicit, "dscr_explicit_test");
+	unsigned long orig_dscr_default = 0;
+	int err = 0;
+
+	if (have_hwcap2(PPC_FEATURE2_DSCR))
+		orig_dscr_default = get_default_dscr();
+
+	err |= test_harness(dscr_explicit_lockstep_test, "dscr_explicit_lockstep_test");
+	err |= test_harness(dscr_explicit_random_test, "dscr_explicit_random_test");
+
+	if (have_hwcap2(PPC_FEATURE2_DSCR))
+		set_default_dscr(orig_dscr_default);
+
+	return err;
 }
-- 
2.39.2

[PATCH v2 5/7] selftests/powerpc/dscr: Improve DSCR explicit random test case

[Benjamin Gray]

The tests currently have a single writer thread updating the system
DSCR with a 1/1000 chance looped only 100 times. So only around one in
10 runs actually do anything.

* Add multiple threads to the dscr_explicit_random_test case.
* Use a barrier to make all the threads start work as simultaneously as
  possible.
* Use a rwlock and make all threads have a reasonable chance to write to
  the DSCR on each iteration.
  PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP is used to prevent
  writers from starving while all the other threads keep reading.
  Logging the reads/writes shows a decent mix across the whole test.
* Allow all threads a chance to write.
* Make the chance of writing more likely.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
---
 tools/testing/selftests/powerpc/dscr/dscr.h   |   4 -
 .../powerpc/dscr/dscr_default_test.c          | 140 ++++++++----------
 .../powerpc/dscr/dscr_explicit_test.c         |  84 +++++++----
 3 files changed, 113 insertions(+), 115 deletions(-)

diff --git a/tools/testing/selftests/powerpc/dscr/dscr.h b/tools/testing/selftests/powerpc/dscr/dscr.h
index 2c54998d4715..b281659071e8 100644
--- a/tools/testing/selftests/powerpc/dscr/dscr.h
+++ b/tools/testing/selftests/powerpc/dscr/dscr.h
@@ -86,8 +86,4 @@ void set_default_dscr(unsigned long val)
 	}
 }
 
-double uniform_deviate(int seed)
-{
-	return seed * (1.0 / (RAND_MAX + 1.0));
-}
 #endif	/* _SELFTESTS_POWERPC_DSCR_DSCR_H */
diff --git a/tools/testing/selftests/powerpc/dscr/dscr_default_test.c b/tools/testing/selftests/powerpc/dscr/dscr_default_test.c
index 18e533d46c9a..60ab02525b79 100644
--- a/tools/testing/selftests/powerpc/dscr/dscr_default_test.c
+++ b/tools/testing/selftests/powerpc/dscr/dscr_default_test.c
@@ -69,105 +69,85 @@ int dscr_default_lockstep_test(void)
 	return 0;
 }
 
-static unsigned long dscr;		/* System DSCR default */
-static unsigned long sequence;
-static unsigned long result[THREADS];
-
-static void *do_test(void *in)
+struct random_thread_args {
+	pthread_t thread_id;
+	unsigned long *expected_system_dscr;
+	pthread_rwlock_t *rw_lock;
+	pthread_barrier_t *barrier;
+};
+
+static void *dscr_default_random_thread(void *in)
 {
-	unsigned long thread = (unsigned long)in;
-	unsigned long i;
-
-	for (i = 0; i < COUNT; i++) {
-		unsigned long d, cur_dscr, cur_dscr_usr;
-		unsigned long s1, s2;
-
-		s1 = READ_ONCE(sequence);
-		if (s1 & 1)
-			continue;
-		rmb();
-
-		d = dscr;
-		cur_dscr = get_dscr();
-		cur_dscr_usr = get_dscr_usr();
-
-		rmb();
-		s2 = sequence;
+	struct random_thread_args *args = (struct random_thread_args *)in;
+	unsigned long *expected_dscr_p = args->expected_system_dscr;
+	pthread_rwlock_t *rw_lock = args->rw_lock;
+	int err;
 
-		if (s1 != s2)
-			continue;
+	srand(gettid());
 
-		if (cur_dscr != d) {
-			fprintf(stderr, "thread %ld kernel DSCR should be %ld "
-				"but is %ld\n", thread, d, cur_dscr);
-			result[thread] = 1;
-			pthread_exit(&result[thread]);
-		}
+	err = pthread_barrier_wait(args->barrier);
+	FAIL_IF_EXIT(err != 0 && err != PTHREAD_BARRIER_SERIAL_THREAD);
 
-		if (cur_dscr_usr != d) {
-			fprintf(stderr, "thread %ld user DSCR should be %ld "
-				"but is %ld\n", thread, d, cur_dscr_usr);
-			result[thread] = 1;
-			pthread_exit(&result[thread]);
+	for (int i = 0; i < COUNT; i++) {
+		unsigned long expected_dscr;
+		unsigned long current_dscr;
+		unsigned long current_dscr_usr;
+
+		FAIL_IF_EXIT(pthread_rwlock_rdlock(rw_lock));
+		expected_dscr = *expected_dscr_p;
+		current_dscr = get_dscr();
+		current_dscr_usr = get_dscr_usr();
+		FAIL_IF_EXIT(pthread_rwlock_unlock(rw_lock));
+
+		FAIL_IF_EXIT(current_dscr != expected_dscr);
+		FAIL_IF_EXIT(current_dscr_usr != expected_dscr);
+
+		if (rand() % 10 == 0) {
+			unsigned long next_dscr;
+
+			FAIL_IF_EXIT(pthread_rwlock_wrlock(rw_lock));
+			next_dscr = (*expected_dscr_p + 1) % DSCR_MAX;
+			set_default_dscr(next_dscr);
+			*expected_dscr_p = next_dscr;
+			FAIL_IF_EXIT(pthread_rwlock_unlock(rw_lock));
 		}
 	}
-	result[thread] = 0;
-	pthread_exit(&result[thread]);
+
+	pthread_exit((void *)0);
 }
 
 int dscr_default_random_test(void)
 {
-	pthread_t threads[THREADS];
-	unsigned long i, *status[THREADS];
+	struct random_thread_args threads[THREADS];
+	unsigned long expected_system_dscr = 0;
+	pthread_rwlockattr_t rwlock_attr;
+	pthread_rwlock_t rw_lock;
+	pthread_barrier_t barrier;
 
 	SKIP_IF(!have_hwcap2(PPC_FEATURE2_DSCR));
 
-	/* Initial DSCR default */
-	dscr = 1;
-	set_default_dscr(dscr);
+	FAIL_IF(pthread_rwlockattr_setkind_np(&rwlock_attr,
+					      PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP));
+	FAIL_IF(pthread_rwlock_init(&rw_lock, &rwlock_attr));
+	FAIL_IF(pthread_barrier_init(&barrier, NULL, THREADS));
 
-	/* Spawn all testing threads */
-	for (i = 0; i < THREADS; i++) {
-		if (pthread_create(&threads[i], NULL, do_test, (void *)i)) {
-			perror("pthread_create() failed");
-			return 1;
-		}
-	}
+	set_default_dscr(expected_system_dscr);
 
-	srand(getpid());
+	for (int i = 0; i < THREADS; i++) {
+		threads[i].expected_system_dscr = &expected_system_dscr;
+		threads[i].rw_lock = &rw_lock;
+		threads[i].barrier = &barrier;
 
-	/* Keep changing the DSCR default */
-	for (i = 0; i < COUNT; i++) {
-		double ret = uniform_deviate(rand());
-
-		if (ret < 0.0001) {
-			sequence++;
-			wmb();
-
-			dscr++;
-			if (dscr > DSCR_MAX)
-				dscr = 0;
-
-			set_default_dscr(dscr);
-
-			wmb();
-			sequence++;
-		}
+		FAIL_IF(pthread_create(&threads[i].thread_id, NULL,
+				       dscr_default_random_thread, (void *)&threads[i]));
 	}
 
-	/* Individual testing thread exit status */
-	for (i = 0; i < THREADS; i++) {
-		if (pthread_join(threads[i], (void **)&(status[i]))) {
-			perror("pthread_join() failed");
-			return 1;
-		}
+	for (int i = 0; i < THREADS; i++)
+		FAIL_IF(pthread_join(threads[i].thread_id, NULL));
+
+	FAIL_IF(pthread_barrier_destroy(&barrier));
+	FAIL_IF(pthread_rwlock_destroy(&rw_lock));
 
-		if (*status[i]) {
-			printf("%ldth thread failed to join with %ld status\n",
-								i, *status[i]);
-			return 1;
-		}
-	}
 	return 0;
 }
 
diff --git a/tools/testing/selftests/powerpc/dscr/dscr_explicit_test.c b/tools/testing/selftests/powerpc/dscr/dscr_explicit_test.c
index 3b98b9a88207..e2268e9183a8 100644
--- a/tools/testing/selftests/powerpc/dscr/dscr_explicit_test.c
+++ b/tools/testing/selftests/powerpc/dscr/dscr_explicit_test.c
@@ -86,50 +86,72 @@ int dscr_explicit_lockstep_test(void)
 	return 0;
 }
 
-int dscr_explicit_random_test(void)
+struct random_thread_args {
+	pthread_t thread_id;
+	bool do_yields;
+	pthread_barrier_t *barrier;
+};
+
+void *dscr_explicit_random_thread(void *in)
 {
-	unsigned long i, dscr = 0;
+	struct random_thread_args *args = (struct random_thread_args *)in;
+	unsigned long expected_dscr = 0;
+	int err;
 
-	SKIP_IF(!have_hwcap2(PPC_FEATURE2_DSCR));
+	srand(gettid());
 
-	srand(getpid());
-	set_dscr(dscr);
+	err = pthread_barrier_wait(args->barrier);
+	FAIL_IF_EXIT(err != 0 && err != PTHREAD_BARRIER_SERIAL_THREAD);
 
-	for (i = 0; i < COUNT; i++) {
-		unsigned long cur_dscr, cur_dscr_usr;
-		double ret = uniform_deviate(rand());
+	for (int i = 0; i < COUNT; i++) {
+		expected_dscr = rand() % DSCR_MAX;
+		set_dscr(expected_dscr);
 
-		if (ret < 0.001) {
-			dscr++;
-			if (dscr > DSCR_MAX)
-				dscr = 0;
+		for (int j = rand() % 5; j > 0; --j) {
+			FAIL_IF_EXIT(get_dscr() != expected_dscr);
+			FAIL_IF_EXIT(get_dscr_usr() != expected_dscr);
 
-			set_dscr(dscr);
+			if (args->do_yields && rand() % 2)
+				sched_yield();
 		}
 
-		cur_dscr = get_dscr();
-		if (cur_dscr != dscr) {
-			fprintf(stderr, "Kernel DSCR should be %ld but "
-					"is %ld\n", dscr, cur_dscr);
-			return 1;
-		}
+		expected_dscr = rand() % DSCR_MAX;
+		set_dscr_usr(expected_dscr);
 
-		ret = uniform_deviate(rand());
-		if (ret < 0.001) {
-			dscr++;
-			if (dscr > DSCR_MAX)
-				dscr = 0;
+		for (int j = rand() % 5; j > 0; --j) {
+			FAIL_IF_EXIT(get_dscr() != expected_dscr);
+			FAIL_IF_EXIT(get_dscr_usr() != expected_dscr);
 
-			set_dscr_usr(dscr);
+			if (args->do_yields && rand() % 2)
+				sched_yield();
 		}
+	}
 
-		cur_dscr_usr = get_dscr_usr();
-		if (cur_dscr_usr != dscr) {
-			fprintf(stderr, "User DSCR should be %ld but "
-					"is %ld\n", dscr, cur_dscr_usr);
-			return 1;
-		}
+	return NULL;
+}
+
+int dscr_explicit_random_test(void)
+{
+	struct random_thread_args threads[THREADS];
+	pthread_barrier_t barrier;
+
+	SKIP_IF(!have_hwcap2(PPC_FEATURE2_DSCR));
+
+	FAIL_IF(pthread_barrier_init(&barrier, NULL, THREADS));
+
+	for (int i = 0; i < THREADS; i++) {
+		threads[i].do_yields = i % 2 == 0;
+		threads[i].barrier = &barrier;
+
+		FAIL_IF(pthread_create(&threads[i].thread_id, NULL,
+				       dscr_explicit_random_thread, (void *)&threads[i]));
 	}
+
+	for (int i = 0; i < THREADS; i++)
+		FAIL_IF(pthread_join(threads[i].thread_id, NULL));
+
+	FAIL_IF(pthread_barrier_destroy(&barrier));
+
 	return 0;
 }
 
-- 
2.39.2

[PATCH v2 6/7] selftests/powerpc/dscr: Speed up DSCR sysfs tests

[Benjamin Gray]

This test case is extremely slow, taking around a minute compared to
most of the other DSCR tests taking a second at most. Perf shows most
time is spent by the kernel switching to each CPU it reads in
/sys/devices/system/cpu. This switching is an unavoidable consequnce
of reading all the .../cpuN/dscr values.

Remove the outer iteration loop from this test case, reducing the reads
from 1600 to 16. This still updates the DSCR 16 times and verifies on
every CPU each time, so I do not expect the lower coverage to be
meaningful. The speedup is significant: back down to ~1 second like the
other tests.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
---
 .../testing/selftests/powerpc/dscr/dscr_sysfs_test.c  | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/powerpc/dscr/dscr_sysfs_test.c b/tools/testing/selftests/powerpc/dscr/dscr_sysfs_test.c
index 4f1fef6198fc..e7cd0d6b1fad 100644
--- a/tools/testing/selftests/powerpc/dscr/dscr_sysfs_test.c
+++ b/tools/testing/selftests/powerpc/dscr/dscr_sysfs_test.c
@@ -67,17 +67,14 @@ static int check_all_cpu_dscr_defaults(unsigned long val)
 int dscr_sysfs(void)
 {
 	unsigned long orig_dscr_default;
-	int i, j;
 
 	SKIP_IF(!have_hwcap2(PPC_FEATURE2_DSCR));
 
 	orig_dscr_default = get_default_dscr();
-	for (i = 0; i < COUNT; i++) {
-		for (j = 0; j < DSCR_MAX; j++) {
-			set_default_dscr(j);
-			if (check_all_cpu_dscr_defaults(j))
-				goto fail;
-		}
+	for (int i = 0; i < DSCR_MAX; i++) {
+		set_default_dscr(i);
+		if (check_all_cpu_dscr_defaults(i))
+			goto fail;
 	}
 	set_default_dscr(orig_dscr_default);
 	return 0;
-- 
2.39.2

[PATCH v2 7/7] selftests/powerpc/dscr: Restore timeout to DSCR selftests

[Benjamin Gray]

Reducing the time taken by dscr_sysfs_test.c allows restoring the
default timeout, which was removed in
commit 850507f30c38 ("selftests/powerpc: Turn off timeout setting for
benchmarks, dscr, signal, tm") because that test took too long.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
---
 tools/testing/selftests/powerpc/dscr/Makefile | 2 --
 tools/testing/selftests/powerpc/dscr/settings | 1 -
 2 files changed, 3 deletions(-)
 delete mode 100644 tools/testing/selftests/powerpc/dscr/settings

diff --git a/tools/testing/selftests/powerpc/dscr/Makefile b/tools/testing/selftests/powerpc/dscr/Makefile
index b29a8863a734..9289d5febe1e 100644
--- a/tools/testing/selftests/powerpc/dscr/Makefile
+++ b/tools/testing/selftests/powerpc/dscr/Makefile
@@ -3,8 +3,6 @@ TEST_GEN_PROGS := dscr_default_test dscr_explicit_test dscr_user_test	\
 	      dscr_inherit_test dscr_inherit_exec_test dscr_sysfs_test	\
 	      dscr_sysfs_thread_test
 
-TEST_FILES := settings
-
 top_srcdir = ../../../../..
 include ../../lib.mk
 
diff --git a/tools/testing/selftests/powerpc/dscr/settings b/tools/testing/selftests/powerpc/dscr/settings
deleted file mode 100644
index e7b9417537fb..000000000000
--- a/tools/testing/selftests/powerpc/dscr/settings
+++ /dev/null
@@ -1 +0,0 @@
-timeout=0
-- 
2.39.2

Re: [PATCH v2 0/7] Update DSCR tests

[Michael Ellerman]

On Thu, 06 Apr 2023 14:33:13 +1000, Benjamin Gray wrote:
> The randomness based DSCR tests currently have a low probability of doing
> any writes to the DSCR, making them inefficient in uncovering bugs.
> 
> This series adds lockstep variants to these RNG tests, to ensure the happy
> path is always tested, and improves the randomness and size of the RNG
> tests.
> 
> [...]

Applied to powerpc/next.

[1/7] selftests/powerpc/dscr: Correct typos
      https://git.kernel.org/powerpc/c/15f0c2601e141e3c01c8dc3368b81181bc1c9228
[2/7] selftests/powerpc: Move bind_to_cpu() to utils.h
      https://git.kernel.org/powerpc/c/c97b2fc6627e1c26a3a84633e135322918a1e592
[3/7] selftests/powerpc: Allow bind_to_cpu() to automatically pick CPU
      https://git.kernel.org/powerpc/c/6ff4dc25483f3f49d1db48af28d4c485fc77bd21
[4/7] selftests/powerpc/dscr: Add lockstep test cases to DSCR explicit tests
      https://git.kernel.org/powerpc/c/fda8158870063b99b88a0904bbb95188973b4297
[5/7] selftests/powerpc/dscr: Improve DSCR explicit random test case
      https://git.kernel.org/powerpc/c/3067b89ab62305c54ec15b00a2c4dbaf64809c59
[6/7] selftests/powerpc/dscr: Speed up DSCR sysfs tests
      https://git.kernel.org/powerpc/c/c14a9d0a79d4fb83c4e9e8cadc5cb094f41d01d0
[7/7] selftests/powerpc/dscr: Restore timeout to DSCR selftests
      https://git.kernel.org/powerpc/c/ae7312c09014fceb782a92cfb934e973f08b338f

cheers