[Qemu-devel] [PATCH v2] rcu tests: fix compilation on 32-bit ppc

[Paolo Bonzini]

32-bit PPC cannot do atomic operations on long long.  Inside the loops,
we are already using local counters that are summed at the end of
the run---with some exceptions (rcu_stress_count for rcutorture,
n_nodes for test-rcu-list): fix them to use the same technique.
For test-rcu-list, remove the mostly unused member "val" from the
list.  Then, use a mutex to protect the global counts.

Performance does not matter there because every thread will only enter
the critical section once.

Remaining uses of atomic instructions are for ints or pointers.

Reported-by: Andreas Faerber <address@hidden>
Signed-off-by: Paolo Bonzini <address@hidden>
---
 tests/rcutorture.c    | 20 ++++++++++++++++----
 tests/test-rcu-list.c | 42 ++++++++++++++++++++++--------------------
 2 files changed, 38 insertions(+), 24 deletions(-)

diff --git a/tests/rcutorture.c b/tests/rcutorture.c
index 60a2ccf..d6b304d 100644
--- a/tests/rcutorture.c
+++ b/tests/rcutorture.c
@@ -82,6 +82,7 @@ static volatile int goflag = GOFLAG_INIT;
 #define RCU_READ_RUN 1000
 
 #define NR_THREADS 100
+static QemuMutex counts_mutex;
 static QemuThread threads[NR_THREADS];
 static struct rcu_reader_data *data[NR_THREADS];
 static int n_threads;
@@ -130,7 +131,9 @@ static void *rcu_read_perf_test(void *arg)
         }
         n_reads_local += RCU_READ_RUN;
     }
-    atomic_add(&n_reads, n_reads_local);
+    qemu_mutex_lock(&counts_mutex);
+    n_reads += n_reads_local;
+    qemu_mutex_unlock(&counts_mutex);
 
     rcu_unregister_thread();
     return NULL;
@@ -151,7 +154,9 @@ static void *rcu_update_perf_test(void *arg)
         synchronize_rcu();
         n_updates_local++;
     }
-    atomic_add(&n_updates, n_updates_local);
+    qemu_mutex_lock(&counts_mutex);
+    n_updates += n_updates_local;
+    qemu_mutex_unlock(&counts_mutex);
 
     rcu_unregister_thread();
     return NULL;
@@ -241,6 +246,7 @@ static void *rcu_read_stress_test(void *arg)
     struct rcu_stress *p;
     int pc;
     long long n_reads_local = 0;
+    long long rcu_stress_local[RCU_STRESS_PIPE_LEN + 1] = { 0 };
     volatile int garbage = 0;
 
     rcu_register_thread();
@@ -265,13 +271,18 @@ static void *rcu_read_stress_test(void *arg)
         if ((pc > RCU_STRESS_PIPE_LEN) || (pc < 0)) {
             pc = RCU_STRESS_PIPE_LEN;
         }
-        atomic_inc(&rcu_stress_count[pc]);
+        rcu_stress_local[pc]++;
         n_reads_local++;
         if ((++itercnt % 0x1000) == 0) {
             synchronize_rcu();
         }
     }
-    atomic_add(&n_reads, n_reads_local);
+    qemu_mutex_lock(&counts_mutex);
+    n_reads += n_reads_local;
+    for (i = 0; i <= RCU_STRESS_PIPE_LEN; i++) {
+        rcu_stress_count[i] += rcu_stress_local[i];
+    }
+    qemu_mutex_unlock(&counts_mutex);
 
     rcu_unregister_thread();
     return NULL;
@@ -419,6 +430,7 @@ int main(int argc, char *argv[])
     int nreaders = 1;
     int duration = 1;
 
+    qemu_mutex_init(&counts_mutex);
     if (argc >= 2 && argv[1][0] == '-') {
         g_test_init(&argc, &argv, NULL);
         if (g_test_quick()) {
diff --git a/tests/test-rcu-list.c b/tests/test-rcu-list.c
index 46b5e26..4430984 100644
--- a/tests/test-rcu-list.c
+++ b/tests/test-rcu-list.c
@@ -35,16 +35,15 @@
  * Test variables.
  */
 
-long long n_reads = 0LL;
-long long n_updates = 0LL;
-long long n_reclaims = 0LL;
-long long n_nodes_removed = 0LL;
-long long n_nodes = 0LL;
-int g_test_in_charge = 0;
+static QemuMutex counts_mutex;
+static long long n_reads = 0LL;
+static long long n_updates = 0LL;
+static long long n_reclaims = 0LL;
+static long long n_nodes_removed = 0LL;
+static long long n_nodes = 0LL;
+static int g_test_in_charge = 0;
 
-int nthreadsrunning;
-
-char argsbuf[64];
+static int nthreadsrunning;
 
 #define GOFLAG_INIT 0
 #define GOFLAG_RUN  1
@@ -92,21 +91,21 @@ static void wait_all_threads(void)
 struct list_element {
     QLIST_ENTRY(list_element) entry;
     struct rcu_head rcu;
-    long long val;
 };
 
 static void reclaim_list_el(struct rcu_head *prcu)
 {
     struct list_element *el = container_of(prcu, struct list_element, rcu);
     g_free(el);
-    atomic_add(&n_reclaims, 1);
+    /* Accessed only from call_rcu thread.  */
+    n_reclaims++;
 }
 
 static QLIST_HEAD(q_list_head, list_element) Q_list_head;
 
 static void *rcu_q_reader(void *arg)
 {
-    long long j, n_reads_local = 0;
+    long long n_reads_local = 0;
     struct list_element *el;
 
     *(struct rcu_reader_data **)arg = &rcu_reader;
@@ -118,8 +117,6 @@ static void *rcu_q_reader(void *arg)
     while (goflag == GOFLAG_RUN) {
         rcu_read_lock();
         QLIST_FOREACH_RCU(el, &Q_list_head, entry) {
-            j = atomic_read(&el->val);
-            (void)j;
             n_reads_local++;
             if (goflag == GOFLAG_STOP) {
                 break;
@@ -129,7 +126,9 @@ static void *rcu_q_reader(void *arg)
 
         g_usleep(100);
     }
-    atomic_add(&n_reads, n_reads_local);
+    qemu_mutex_lock(&counts_mutex);
+    n_reads += n_reads_local;
+    qemu_mutex_unlock(&counts_mutex);
     return NULL;
 }
 
@@ -137,6 +136,7 @@ static void *rcu_q_reader(void *arg)
 static void *rcu_q_updater(void *arg)
 {
     int j, target_el;
+    long long n_nodes_local = 0;
     long long n_updates_local = 0;
     long long n_removed_local = 0;
     struct list_element *el, *prev_el;
@@ -170,8 +170,7 @@ static void *rcu_q_updater(void *arg)
             j++;
             if (target_el == j) {
                 prev_el = g_new(struct list_element, 1);
-                atomic_add(&n_nodes, 1);
-                prev_el->val = atomic_read(&n_nodes);
+                n_nodes += n_nodes_local;
                 QLIST_INSERT_BEFORE_RCU(el, prev_el, entry);
                 break;
             }
@@ -181,8 +180,11 @@ static void *rcu_q_updater(void *arg)
         synchronize_rcu();
     }
     synchronize_rcu();
-    atomic_add(&n_updates, n_updates_local);
-    atomic_add(&n_nodes_removed, n_removed_local);
+    qemu_mutex_lock(&counts_mutex);
+    n_nodes += n_nodes_local;
+    n_updates += n_updates_local;
+    n_nodes_removed += n_removed_local;
+    qemu_mutex_unlock(&counts_mutex);
     return NULL;
 }
 
@@ -194,7 +196,6 @@ static void rcu_qtest_init(void)
     srand(time(0));
     for (i = 0; i < RCU_Q_LEN; i++) {
         new_el = g_new(struct list_element, 1);
-        new_el->val = i;
         QLIST_INSERT_HEAD_RCU(&Q_list_head, new_el, entry);
     }
     atomic_add(&n_nodes, RCU_Q_LEN);
@@ -277,6 +278,7 @@ int main(int argc, char *argv[])
 {
     int duration = 0, readers = 0;
 
+    qemu_mutex_init(&counts_mutex);
     if (argc >= 2) {
         if (argv[1][0] == '-') {
             g_test_init(&argc, &argv, NULL);
-- 
2.3.3