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authorPaolo Bonzini <pbonzini@redhat.com>2017-02-13 19:12:41 +0100
committerStefan Hajnoczi <stefanha@redhat.com>2017-02-21 11:39:40 +0000
commitc05df34a874706946a918d320e602bb498550838 (patch)
treefeba2bc92fd0c73e7947be386693927f4cf60bbe /tests/test-aio-multithread.c
parent480cff632221dc4d4889bf72dd0f09cd35096bc1 (diff)
test-aio-multithread: add performance comparison with thread-based mutexes
Add two implementations of the same benchmark as the previous patch, but using pthreads. One uses a normal QemuMutex, the other is Linux only and implements a fair mutex based on MCS locks and futexes. This shows that the slower performance of the 5-thread case is due to the fairness of CoMutex, rather than to coroutines. If fairness does not matter, as is the case with two threads, CoMutex can actually be faster than pthreads. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Fam Zheng <famz@redhat.com> Message-id: 20170213181244.16297-4-pbonzini@redhat.com Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Diffstat (limited to 'tests/test-aio-multithread.c')
-rw-r--r--tests/test-aio-multithread.c164
1 files changed, 164 insertions, 0 deletions
diff --git a/tests/test-aio-multithread.c b/tests/test-aio-multithread.c
index 4fa2e9bb74..f11e990568 100644
--- a/tests/test-aio-multithread.c
+++ b/tests/test-aio-multithread.c
@@ -278,6 +278,162 @@ static void test_multi_co_mutex_2_30(void)
test_multi_co_mutex(2, 30);
}
+/* Same test with fair mutexes, for performance comparison. */
+
+#ifdef CONFIG_LINUX
+#include "qemu/futex.h"
+
+/* The nodes for the mutex reside in this structure (on which we try to avoid
+ * false sharing). The head of the mutex is in the "mutex_head" variable.
+ */
+static struct {
+ int next, locked;
+ int padding[14];
+} nodes[NUM_CONTEXTS] __attribute__((__aligned__(64)));
+
+static int mutex_head = -1;
+
+static void mcs_mutex_lock(void)
+{
+ int prev;
+
+ nodes[id].next = -1;
+ nodes[id].locked = 1;
+ prev = atomic_xchg(&mutex_head, id);
+ if (prev != -1) {
+ atomic_set(&nodes[prev].next, id);
+ qemu_futex_wait(&nodes[id].locked, 1);
+ }
+}
+
+static void mcs_mutex_unlock(void)
+{
+ int next;
+ if (nodes[id].next == -1) {
+ if (atomic_read(&mutex_head) == id &&
+ atomic_cmpxchg(&mutex_head, id, -1) == id) {
+ /* Last item in the list, exit. */
+ return;
+ }
+ while (atomic_read(&nodes[id].next) == -1) {
+ /* mcs_mutex_lock did the xchg, but has not updated
+ * nodes[prev].next yet.
+ */
+ }
+ }
+
+ /* Wake up the next in line. */
+ next = nodes[id].next;
+ nodes[next].locked = 0;
+ qemu_futex_wake(&nodes[next].locked, 1);
+}
+
+static void test_multi_fair_mutex_entry(void *opaque)
+{
+ while (!atomic_mb_read(&now_stopping)) {
+ mcs_mutex_lock();
+ counter++;
+ mcs_mutex_unlock();
+ atomic_inc(&atomic_counter);
+ }
+ atomic_dec(&running);
+}
+
+static void test_multi_fair_mutex(int threads, int seconds)
+{
+ int i;
+
+ assert(mutex_head == -1);
+ counter = 0;
+ atomic_counter = 0;
+ now_stopping = false;
+
+ create_aio_contexts();
+ assert(threads <= NUM_CONTEXTS);
+ running = threads;
+ for (i = 0; i < threads; i++) {
+ Coroutine *co1 = qemu_coroutine_create(test_multi_fair_mutex_entry, NULL);
+ aio_co_schedule(ctx[i], co1);
+ }
+
+ g_usleep(seconds * 1000000);
+
+ atomic_mb_set(&now_stopping, true);
+ while (running > 0) {
+ g_usleep(100000);
+ }
+
+ join_aio_contexts();
+ g_test_message("%d iterations/second\n", counter / seconds);
+ g_assert_cmpint(counter, ==, atomic_counter);
+}
+
+static void test_multi_fair_mutex_1(void)
+{
+ test_multi_fair_mutex(NUM_CONTEXTS, 1);
+}
+
+static void test_multi_fair_mutex_10(void)
+{
+ test_multi_fair_mutex(NUM_CONTEXTS, 10);
+}
+#endif
+
+/* Same test with pthread mutexes, for performance comparison and
+ * portability. */
+
+static QemuMutex mutex;
+
+static void test_multi_mutex_entry(void *opaque)
+{
+ while (!atomic_mb_read(&now_stopping)) {
+ qemu_mutex_lock(&mutex);
+ counter++;
+ qemu_mutex_unlock(&mutex);
+ atomic_inc(&atomic_counter);
+ }
+ atomic_dec(&running);
+}
+
+static void test_multi_mutex(int threads, int seconds)
+{
+ int i;
+
+ qemu_mutex_init(&mutex);
+ counter = 0;
+ atomic_counter = 0;
+ now_stopping = false;
+
+ create_aio_contexts();
+ assert(threads <= NUM_CONTEXTS);
+ running = threads;
+ for (i = 0; i < threads; i++) {
+ Coroutine *co1 = qemu_coroutine_create(test_multi_mutex_entry, NULL);
+ aio_co_schedule(ctx[i], co1);
+ }
+
+ g_usleep(seconds * 1000000);
+
+ atomic_mb_set(&now_stopping, true);
+ while (running > 0) {
+ g_usleep(100000);
+ }
+
+ join_aio_contexts();
+ g_test_message("%d iterations/second\n", counter / seconds);
+ g_assert_cmpint(counter, ==, atomic_counter);
+}
+
+static void test_multi_mutex_1(void)
+{
+ test_multi_mutex(NUM_CONTEXTS, 1);
+}
+
+static void test_multi_mutex_10(void)
+{
+ test_multi_mutex(NUM_CONTEXTS, 10);
+}
+
/* End of tests. */
int main(int argc, char **argv)
@@ -290,10 +446,18 @@ int main(int argc, char **argv)
g_test_add_func("/aio/multi/schedule", test_multi_co_schedule_1);
g_test_add_func("/aio/multi/mutex/contended", test_multi_co_mutex_1);
g_test_add_func("/aio/multi/mutex/handoff", test_multi_co_mutex_2_3);
+#ifdef CONFIG_LINUX
+ g_test_add_func("/aio/multi/mutex/mcs", test_multi_fair_mutex_1);
+#endif
+ g_test_add_func("/aio/multi/mutex/pthread", test_multi_mutex_1);
} else {
g_test_add_func("/aio/multi/schedule", test_multi_co_schedule_10);
g_test_add_func("/aio/multi/mutex/contended", test_multi_co_mutex_10);
g_test_add_func("/aio/multi/mutex/handoff", test_multi_co_mutex_2_30);
+#ifdef CONFIG_LINUX
+ g_test_add_func("/aio/multi/mutex/mcs", test_multi_fair_mutex_10);
+#endif
+ g_test_add_func("/aio/multi/mutex/pthread", test_multi_mutex_10);
}
return g_test_run();
}