[Qemu-devel] [kvm-unit-tests PATCH v5 11/11] new: arm/barrier-test for memory barriers

["Alex Bennée" <alex.bennee@linaro.org>]

From: Alex Bennée <alex@bennee.com>

This test has been written mainly to stress multi-threaded TCG behaviour
but will demonstrate failure by default on real hardware. The test takes
the following parameters:

  - "lock" use GCC's locking semantics
  - "excl" use load/store exclusive semantics
  - "acqrel" use acquire/release semantics

Currently excl/acqrel lock up on MTTCG

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
---
 arm/barrier-test.c           | 206 +++++++++++++++++++++++++++++++++++++++++++
 config/config-arm-common.mak |   2 +
 2 files changed, 208 insertions(+)
 create mode 100644 arm/barrier-test.c

diff --git a/arm/barrier-test.c b/arm/barrier-test.c
new file mode 100644
index 0000000..53d690b
--- /dev/null
+++ b/arm/barrier-test.c
@@ -0,0 +1,206 @@
+#include <libcflat.h>
+#include <asm/smp.h>
+#include <asm/cpumask.h>
+#include <asm/barrier.h>
+#include <asm/mmu.h>
+
+#include <prng.h>
+
+#define MAX_CPUS 4
+
+/* How many increments to do */
+static int increment_count = 10000000;
+
+
+/* shared value, we use the alignment to ensure the global_lock value
+ * doesn't share a page */
+static unsigned int shared_value;
+
+/* PAGE_SIZE * uint32_t means we span several pages */
+static uint32_t memory_array[PAGE_SIZE];
+
+__attribute__((aligned(PAGE_SIZE))) static unsigned int per_cpu_value[MAX_CPUS];
+__attribute__((aligned(PAGE_SIZE))) static cpumask_t smp_test_complete;
+__attribute__((aligned(PAGE_SIZE))) static int global_lock;
+
+struct isaac_ctx prng_context[MAX_CPUS];
+
+void (*inc_fn)(void);
+
+static void lock(int *lock_var)
+{
+	while (__sync_lock_test_and_set(lock_var, 1));
+}
+static void unlock(int *lock_var)
+{
+	__sync_lock_release(lock_var);
+}
+
+static void increment_shared(void)
+{
+	shared_value++;
+}
+
+static void increment_shared_with_lock(void)
+{
+	lock(&global_lock);
+	shared_value++;
+	unlock(&global_lock);
+}
+
+static void increment_shared_with_excl(void)
+{
+#if defined (__LP64__) || defined (_LP64)
+	asm volatile(
+	"1:	ldxr	w0, [%[sptr]]\n"
+	"	add     w0, w0, #0x1\n"
+	"	stxr	w1, w0, [%[sptr]]\n"
+	"	cbnz	w1, 1b\n"
+	: /* out */
+	: [sptr] "r" (&shared_value) /* in */
+	: "w0", "w1", "cc");
+#else
+	asm volatile(
+	"1:	ldrex	r0, [%[sptr]]\n"
+	"	add     r0, r0, #0x1\n"
+	"	strexeq	r1, r0, [%[sptr]]\n"
+	"	cmpeq	r1, #0\n"
+	"	bne	1b\n"
+	: /* out */
+	: [sptr] "r" (&shared_value) /* in */
+	: "r0", "r1", "cc");
+#endif
+}
+
+static void increment_shared_with_acqrel(void)
+{
+#if defined (__LP64__) || defined (_LP64)
+	asm volatile(
+	"	ldar	w0, [%[sptr]]\n"
+	"	add     w0, w0, #0x1\n"
+	"	str	w0, [%[sptr]]\n"
+	: /* out */
+	: [sptr] "r" (&shared_value) /* in */
+	: "w0");
+#else
+	/* ARMv7 has no acquire/release semantics but we
+	 * can ensure the results of the write are propagated
+	 * with the use of barriers.
+	 */
+	asm volatile(
+	"1:	ldrex	r0, [%[sptr]]\n"
+	"	add     r0, r0, #0x1\n"
+	"	strexeq	r1, r0, [%[sptr]]\n"
+	"	cmpeq	r1, #0\n"
+	"	bne	1b\n"
+	"	dmb\n"
+	: /* out */
+	: [sptr] "r" (&shared_value) /* in */
+	: "r0", "r1", "cc");
+#endif
+
+}
+
+/* The idea of this is just to generate some random load/store
+ * activity which may or may not race with an un-barried incremented
+ * of the shared counter
+ */
+static void shuffle_memory(int cpu)
+{
+	int i;
+	uint32_t lspat = isaac_next_uint32(&prng_context[cpu]);
+	uint32_t seq = isaac_next_uint32(&prng_context[cpu]);
+	int count = seq & 0x1f;
+	uint32_t val=0;
+
+	seq >>= 5;
+
+	for (i=0; i<count; i++) {
+		int index = seq & ~PAGE_MASK;
+		if (lspat & 1) {
+			val ^= memory_array[index];
+		} else {
+			memory_array[index] = val;
+		}
+		seq >>= PAGE_SHIFT;
+		seq ^= lspat;
+		lspat >>= 1;
+	}
+
+}
+
+static void do_increment(void)
+{
+	int i;
+	int cpu = smp_processor_id();
+
+	printf("CPU%d online\n", cpu);
+
+	for (i=0; i < increment_count; i++) {
+		per_cpu_value[cpu]++;
+		inc_fn();
+
+		shuffle_memory(cpu);
+	}
+
+	printf("CPU%d: Done, %d incs\n", cpu, per_cpu_value[cpu]);
+
+	cpumask_set_cpu(cpu, &smp_test_complete);
+	if (cpu != 0)
+		halt();
+}
+
+int main(int argc, char **argv)
+{
+	int cpu;
+	unsigned int i, sum = 0;
+	static const unsigned char seed[] = "myseed";
+
+	inc_fn = &increment_shared;
+
+	isaac_init(&prng_context[0], &seed[0], sizeof(seed));
+
+	for (i=0; i<argc; i++) {
+		char *arg = argv[i];
+
+		if (strcmp(arg, "lock") == 0) {
+			inc_fn = &increment_shared_with_lock;
+			report_prefix_push("lock");
+		} else if (strcmp(arg, "excl") == 0) {
+			inc_fn = &increment_shared_with_excl;
+			report_prefix_push("excl");
+		} else if (strcmp(arg, "acqrel") == 0) {
+			inc_fn = &increment_shared_with_acqrel;
+			report_prefix_push("acqrel");
+		} else {
+			isaac_reseed(&prng_context[0], (unsigned char *) arg, strlen(arg));
+		}
+	}
+
+	/* fill our random page */
+	for (i=0; i<PAGE_SIZE; i++) {
+		memory_array[i] = isaac_next_uint32(&prng_context[0]);
+	}
+
+	for_each_present_cpu(cpu) {
+		uint32_t seed2 = isaac_next_uint32(&prng_context[0]);
+		if (cpu == 0)
+			continue;
+
+		isaac_init(&prng_context[cpu], (unsigned char *) &seed2, sizeof(seed2));
+		smp_boot_secondary(cpu, do_increment);
+	}
+
+	do_increment();
+
+	while (!cpumask_full(&smp_test_complete))
+		cpu_relax();
+
+	/* All CPUs done, do we add up */
+	for_each_present_cpu(cpu) {
+		sum += per_cpu_value[cpu];
+	}
+	report("total incs %d", sum == shared_value, shared_value);
+
+	return report_summary();
+}
diff --git a/config/config-arm-common.mak b/config/config-arm-common.mak
index 67a9dda..af628e6 100644
--- a/config/config-arm-common.mak
+++ b/config/config-arm-common.mak
@@ -12,6 +12,7 @@ endif
 tests-common = $(TEST_DIR)/selftest.flat
 tests-common += $(TEST_DIR)/spinlock-test.flat
 tests-common += $(TEST_DIR)/tlbflush-test.flat
+tests-common += $(TEST_DIR)/barrier-test.flat
 
 utils-common = $(TEST_DIR)/utils/kvm-query
 
@@ -80,3 +81,4 @@ utils: $(utils-common)
 $(TEST_DIR)/selftest.elf: $(cstart.o) $(TEST_DIR)/selftest.o
 $(TEST_DIR)/spinlock-test.elf: $(cstart.o) $(TEST_DIR)/spinlock-test.o
 $(TEST_DIR)/tlbflush-test.elf: $(cstart.o) $(TEST_DIR)/tlbflush-test.o
+$(TEST_DIR)/barrier-test.elf: $(cstart.o) $(TEST_DIR)/barrier-test.o
-- 
2.5.0