1 files changed, 91 insertions, 5 deletions

diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
index 75174c81529a..773219907dd8 100644
--- a/kernel/rcutorture.c
+++ b/kernel/rcutorture.c
@@ -48,9 +48,11 @@
 MODULE_LICENSE("GPL");
 
 static int nreaders = -1;       /* # reader threads, defaults to 4*ncpus */
-static int stat_interval = 0;   /* Interval between stats, in seconds. */
+static int stat_interval;       /* Interval between stats, in seconds. */
                                 /*  Defaults to "only at end of test". */
-static int verbose = 0;         /* Print more debug info. */
+static int verbose;             /* Print more debug info. */
+static int test_no_idle_hz;     /* Test RCU's support for tickless idle CPUs. */
+static int shuffle_interval = 5; /* Interval between shuffles (in sec)*/
 
 MODULE_PARM(nreaders, "i");
 MODULE_PARM_DESC(nreaders, "Number of RCU reader threads");
@@ -58,6 +60,10 @@ MODULE_PARM(stat_interval, "i");
 MODULE_PARM_DESC(stat_interval, "Number of seconds between stats printk()s");
 MODULE_PARM(verbose, "i");
 MODULE_PARM_DESC(verbose, "Enable verbose debugging printk()s");
+MODULE_PARM(test_no_idle_hz, "i");
+MODULE_PARM_DESC(test_no_idle_hz, "Test support for tickless idle CPUs");
+MODULE_PARM(shuffle_interval, "i");
+MODULE_PARM_DESC(shuffle_interval, "Number of seconds between shuffles");
 #define TORTURE_FLAG "rcutorture: "
 #define PRINTK_STRING(s) \
         do { printk(KERN_ALERT TORTURE_FLAG s "\n"); } while (0)
@@ -72,6 +78,7 @@ static int nrealreaders;
 static struct task_struct *writer_task;
 static struct task_struct **reader_tasks;
 static struct task_struct *stats_task;
+static struct task_struct *shuffler_task;
 
 #define RCU_TORTURE_PIPE_LEN 10
 
@@ -375,12 +382,77 @@ rcu_torture_stats(void *arg)
         return 0;
 }
 
+static int rcu_idle_cpu;        /* Force all torture tasks off this CPU */
+
+/* Shuffle tasks such that we allow @rcu_idle_cpu to become idle. A special case
+ * is when @rcu_idle_cpu = -1, when we allow the tasks to run on all CPUs.
+ */
+void rcu_torture_shuffle_tasks(void)
+{
+        cpumask_t tmp_mask = CPU_MASK_ALL;
+        int i;
+
+        lock_cpu_hotplug();
+
+        /* No point in shuffling if there is only one online CPU (ex: UP) */
+        if (num_online_cpus() == 1) {
+                unlock_cpu_hotplug();
+                return;
+        }
+
+        if (rcu_idle_cpu != -1)
+                cpu_clear(rcu_idle_cpu, tmp_mask);
+
+        set_cpus_allowed(current, tmp_mask);
+
+        if (reader_tasks != NULL) {
+                for (i = 0; i < nrealreaders; i++)
+                        if (reader_tasks[i])
+                                set_cpus_allowed(reader_tasks[i], tmp_mask);
+        }
+
+        if (writer_task)
+                set_cpus_allowed(writer_task, tmp_mask);
+
+        if (stats_task)
+                set_cpus_allowed(stats_task, tmp_mask);
+
+        if (rcu_idle_cpu == -1)
+                rcu_idle_cpu = num_online_cpus() - 1;
+        else
+                rcu_idle_cpu--;
+
+        unlock_cpu_hotplug();
+}
+
+/* Shuffle tasks across CPUs, with the intent of allowing each CPU in the
+ * system to become idle at a time and cut off its timer ticks. This is meant
+ * to test the support for such tickless idle CPU in RCU.
+ */
+static int
+rcu_torture_shuffle(void *arg)
+{
+        VERBOSE_PRINTK_STRING("rcu_torture_shuffle task started");
+        do {
+                schedule_timeout_interruptible(shuffle_interval * HZ);
+                rcu_torture_shuffle_tasks();
+        } while (!kthread_should_stop());
+        VERBOSE_PRINTK_STRING("rcu_torture_shuffle task stopping");
+        return 0;
+}
+
 static void
 rcu_torture_cleanup(void)
 {
         int i;
 
         fullstop = 1;
+        if (shuffler_task != NULL) {
+                VERBOSE_PRINTK_STRING("Stopping rcu_torture_shuffle task");
+                kthread_stop(shuffler_task);
+        }
+        shuffler_task = NULL;
+
         if (writer_task != NULL) {
                 VERBOSE_PRINTK_STRING("Stopping rcu_torture_writer task");
                 kthread_stop(writer_task);
@@ -429,9 +501,11 @@ rcu_torture_init(void)
                 nrealreaders = nreaders;
         else
                 nrealreaders = 2 * num_online_cpus();
-        printk(KERN_ALERT TORTURE_FLAG
-               "--- Start of test: nreaders=%d stat_interval=%d verbose=%d\n",
-               nrealreaders, stat_interval, verbose);
+        printk(KERN_ALERT TORTURE_FLAG "--- Start of test: nreaders=%d "
+                "stat_interval=%d verbose=%d test_no_idle_hz=%d "
+                "shuffle_interval = %d\n",
+                nrealreaders, stat_interval, verbose, test_no_idle_hz,
+                shuffle_interval);
         fullstop = 0;
 
         /* Set up the freelist. */
@@ -501,6 +575,18 @@ rcu_torture_init(void)
                         goto unwind;
                 }
         }
+        if (test_no_idle_hz) {
+                rcu_idle_cpu = num_online_cpus() - 1;
+                /* Create the shuffler thread */
+                shuffler_task = kthread_run(rcu_torture_shuffle, NULL,
+                                          "rcu_torture_shuffle");
+                if (IS_ERR(shuffler_task)) {
+                        firsterr = PTR_ERR(shuffler_task);
+                        VERBOSE_PRINTK_ERRSTRING("Failed to create shuffler");
+                        shuffler_task = NULL;
+                        goto unwind;
+                }
+        }
         return 0;
 
 unwind: