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
- "atomic" use GCC's __atomic primitives
- "wfelock" use WaitForEvent sleep
- "excl" use load/store exclusive semantics
Also two more options allow the test to be tweaked
- "noshuffle" disables the memory shuffling
- "count=%ld" set your own per-CPU increment count
Signed-off-by: Alex Bennée <alex.bennee@xxxxxxxxxx>
---
v2
- Don't use thumb style strexeq stuff
- Add atomic and wfelock tests
- Add count/noshuffle test controls
- Move barrier tests to separate test file
v4
- fix up unitests.cfg to use correct test name
- move into "locking" group, remove barrier tests
- use a table to add tests, mark which are expected to work
- correctly report XFAIL
v5
- max out at -smp 4 in unittest.cfg
v7
- make test control flags bools
- default the count to 100000 (so it doesn't timeout)
---
arm/Makefile.common | 2 +
arm/locking-test.c | 302 ++++++++++++++++++++++++++++++++++++++++++++++++++++
arm/unittests.cfg | 34 ++++++
3 files changed, 338 insertions(+)
create mode 100644 arm/locking-test.c
diff --git a/arm/Makefile.common b/arm/Makefile.common
index 528166d..eb4cfdf 100644
--- a/arm/Makefile.common
+++ b/arm/Makefile.common
@@ -15,6 +15,7 @@ tests-common += $(TEST_DIR)/pci-test.flat
tests-common += $(TEST_DIR)/gic.flat
tests-common += $(TEST_DIR)/tlbflush-code.flat
tests-common += $(TEST_DIR)/tlbflush-data.flat
+tests-common += $(TEST_DIR)/locking-test.flat
all: test_cases
@@ -85,3 +86,4 @@ test_cases: $(generated_files) $(tests-common) $(tests)
$(TEST_DIR)/selftest.o $(cstart.o): $(asm-offsets)
$(TEST_DIR)/tlbflush-code.elf: $(cstart.o) $(TEST_DIR)/tlbflush-code.o
$(TEST_DIR)/tlbflush-data.elf: $(cstart.o) $(TEST_DIR)/tlbflush-data.o
+$(TEST_DIR)/locking-test.elf: $(cstart.o) $(TEST_DIR)/locking-test.o
diff --git a/arm/locking-test.c b/arm/locking-test.c
new file mode 100644
index 0000000..f10c61b
--- /dev/null
+++ b/arm/locking-test.c
@@ -0,0 +1,302 @@
+#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 8
+
+/* Test definition structure
+ *
+ * A simple structure that describes the test name, expected pass and
+ * increment function.
+ */
+
+/* Function pointers for test */
+typedef void (*inc_fn)(int cpu);
+
+typedef struct {
+ const char *test_name;
+ bool should_pass;
+ inc_fn main_fn;
+} test_descr_t;
+
+/* How many increments to do */
+static int increment_count = 1000000;
+static bool do_shuffle = true;
+
+/* Shared value all the tests attempt to safely increment using
+ * various forms of atomic locking and exclusive behaviour.
+ */
+static unsigned int shared_value;
+
+/* PAGE_SIZE * uint32_t means we span several pages */
+__attribute__((aligned(PAGE_SIZE))) static uint32_t memory_array[PAGE_SIZE];
+
+/* We use the alignment of the following to ensure accesses to locking
+ * and synchronisation primatives don't interfere with the page of the
+ * shared value
+ */
+__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))) struct isaac_ctx prng_context[MAX_CPUS];
+
+/* Some of the approaches use a global lock to prevent contention. */
+static int global_lock;
+
+/* In any SMP setting this *should* fail due to cores stepping on
+ * each other updating the shared variable
+ */
+static void increment_shared(int cpu)
+{
+ (void)cpu;
+
+ shared_value++;
+}
+
+/* GCC __sync primitives are deprecated in favour of __atomic */
+static void increment_shared_with_lock(int cpu)
+{
+ (void)cpu;
+
+ while (__sync_lock_test_and_set(&global_lock, 1));
+ shared_value++;
+ __sync_lock_release(&global_lock);
+}
+
+/* In practice even __ATOMIC_RELAXED uses ARM's ldxr/stex exclusive
+ * semantics */
+static void increment_shared_with_atomic(int cpu)
+{
+ (void)cpu;
+
+ __atomic_add_fetch(&shared_value, 1, __ATOMIC_SEQ_CST);
+}
+
+
+/*
+ * Load/store exclusive with WFE (wait-for-event)
+ *
+ * See ARMv8 ARM examples:
+ * Use of Wait For Event (WFE) and Send Event (SEV) with locks
+ */
+
+static void increment_shared_with_wfelock(int cpu)
+{
+ (void)cpu;
+
+#if defined(__aarch64__)
+ asm volatile(
+ " mov w1, #1\n"
+ " sevl\n"
+ " prfm PSTL1KEEP, [%[lock]]\n"
+ "1: wfe\n"
+ " ldaxr w0, [%[lock]]\n"
+ " cbnz w0, 1b\n"
+ " stxr w0, w1, [%[lock]]\n"
+ " cbnz w0, 1b\n"
+ /* lock held */
+ " ldr w0, [%[sptr]]\n"
+ " add w0, w0, #0x1\n"
+ " str w0, [%[sptr]]\n"
+ /* now release */
+ " stlr wzr, [%[lock]]\n"
+ : /* out */
+ : [lock] "r" (&global_lock), [sptr] "r" (&shared_value) /* in */
+ : "w0", "w1", "cc");
+#else
+ asm volatile(
+ " mov r1, #1\n"
+ "1: ldrex r0, [%[lock]]\n"
+ " cmp r0, #0\n"
+ " wfene\n"
+ " strexeq r0, r1, [%[lock]]\n"
+ " cmpeq r0, #0\n"
+ " bne 1b\n"
+ " dmb\n"
+ /* lock held */
+ " ldr r0, [%[sptr]]\n"
+ " add r0, r0, #0x1\n"
+ " str r0, [%[sptr]]\n"
+ /* now release */
+ " mov r0, #0\n"
+ " dmb\n"
+ " str r0, [%[lock]]\n"
+ " dsb\n"
+ " sev\n"
+ : /* out */
+ : [lock] "r" (&global_lock), [sptr] "r" (&shared_value) /* in */
+ : "r0", "r1", "cc");
+#endif
+}
+
+
+/*
+ * Hand-written version of the load/store exclusive
+ */
+static void increment_shared_with_excl(int cpu)
+{
+ (void)cpu;
+
+#if defined(__aarch64__)
+ 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"
+ " strex r1, r0, [%[sptr]]\n"
+ " cmp r1, #0\n"
+ " bne 1b\n"
+ : /* out */
+ : [sptr] "r" (&shared_value) /* in */
+ : "r0", "r1", "cc");
+#endif
+}
+
+/* Test array */
+static test_descr_t tests[] = {
+ { "none", false, increment_shared },
+ { "lock", true, increment_shared_with_lock },
+ { "atomic", true, increment_shared_with_atomic },
+ { "wfelock", true, increment_shared_with_wfelock },
+ { "excl", true, increment_shared_with_excl }
+};
+
+/* 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 inc_fn increment_function;
+
+static void do_increment(void)
+{
+ int i;
+ int cpu = smp_processor_id();
+
+ printf("CPU%d: online and ++ing\n", cpu);
+
+ for (i=0; i < increment_count; i++) {
+ per_cpu_value[cpu]++;
+ increment_function(cpu);
+
+ if (do_shuffle)
+ 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();
+}
+
+static void setup_and_run_test(test_descr_t *test)
+{
+ unsigned int i, sum = 0;
+ int cpu, cpu_cnt = 0;
+
+ increment_function = test->main_fn;
+
+ /* 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]);
+ cpu_cnt++;
+ 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];
+ }
+
+ if (test->should_pass) {
+ report("total incs %d", sum == shared_value, shared_value);
+ } else {
+ report_xfail("total incs %d", true, sum == shared_value, shared_value);
+ }
+}
+
+int main(int argc, char **argv)
+{
+ static const unsigned char seed[] = "myseed";
+ test_descr_t *test = &tests[0];
+ int i;
+ unsigned int j;
+
+ isaac_init(&prng_context[0], &seed[0], sizeof(seed));
+
+ for (i=0; i<argc; i++) {
+ char *arg = argv[i];
+
+ /* Check for test name */
+ for (j = 0; j < ARRAY_SIZE(tests); j++) {
+ if (strcmp(arg, tests[j].test_name) == 0)
+ test = &tests[j];
+ }
+
+ /* Test modifiers */
+ if (strcmp(arg, "noshuffle") == 0) {
+ do_shuffle = false;
+ report_prefix_push("noshuffle");
+ } else if (strstr(arg, "count=") != NULL) {
+ char *p = strstr(arg, "=");
+ increment_count = atol(p+1);
+ } else {
+ isaac_reseed(&prng_context[0], (unsigned char *) arg, strlen(arg));
+ }
+ }
+
+ if (test) {
+ setup_and_run_test(test);
+ } else {
+ report("Unknown test", false);
+ }
+
+ return report_summary();
+}
diff --git a/arm/unittests.cfg b/arm/unittests.cfg
index 7dc7799..abbfe79 100644
--- a/arm/unittests.cfg
+++ b/arm/unittests.cfg
@@ -108,3 +108,37 @@ smp = $(($MAX_SMP>4?4:$MAX_SMP))
extra_params = -append "page"
groups = tlbflush
+# Locking tests
+[locking::none]
+file = locking-test.flat
+smp = $(($MAX_SMP>4?4:$MAX_SMP))
+groups = locking
+accel = tcg
+
+[locking::lock]
+file = locking-test.flat
+smp = $(($MAX_SMP>4?4:$MAX_SMP))
+extra_params = -append 'lock'
+groups = locking
+accel = tcg
+
+[locking::atomic]
+file = locking-test.flat
+smp = $(($MAX_SMP>4?4:$MAX_SMP))
+extra_params = -append 'atomic'
+groups = locking
+accel = tcg
+
+[locking::wfelock]
+file = locking-test.flat
+smp = $(($MAX_SMP>4?4:$MAX_SMP))
+extra_params = -append 'wfelock'
+groups = locking
+accel = tcg
+
+[locking::excl]
+file = locking-test.flat
+smp = $(($MAX_SMP>4?4:$MAX_SMP))
+extra_params = -append 'excl'
+groups = locking
+accel = tcg
--
2.10.1
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
