rcu: Check the range of jiffies_till_{first,next}_fqs when setting them

Currently, the range of jiffies_till_{first,next}_fqs are checked and
adjusted on and on in the loop of rcu_gp_kthread on runtime.

However, it's enough to check them only when setting them, not every
time in the loop. So make them handled on a setting time via sysfs.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 4915525..7498a41 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -510,8 +510,38 @@ static ulong jiffies_till_first_fqs = ULONG_MAX;
 static ulong jiffies_till_next_fqs = ULONG_MAX;
 static bool rcu_kick_kthreads;
 
-module_param(jiffies_till_first_fqs, ulong, 0644);
-module_param(jiffies_till_next_fqs, ulong, 0644);
+static int param_set_first_fqs_jiffies(const char *val, const struct kernel_param *kp)
+{
+       ulong j;
+       int ret = kstrtoul(val, 0, &j);
+
+       if (!ret)
+               WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : j);
+       return ret;
+}
+
+static int param_set_next_fqs_jiffies(const char *val, const struct kernel_param *kp)
+{
+       ulong j;
+       int ret = kstrtoul(val, 0, &j);
+
+       if (!ret)
+               WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : (j ?: 1));
+       return ret;
+}
+
+static struct kernel_param_ops first_fqs_jiffies_ops = {
+       .set = param_set_first_fqs_jiffies,
+       .get = param_get_ulong,
+};
+
+static struct kernel_param_ops next_fqs_jiffies_ops = {
+       .set = param_set_next_fqs_jiffies,
+       .get = param_get_ulong,
+};
+
+module_param_cb(jiffies_till_first_fqs, &first_fqs_jiffies_ops, &jiffies_till_first_fqs, 0644);
+module_param_cb(jiffies_till_next_fqs, &next_fqs_jiffies_ops, &jiffies_till_next_fqs, 0644);
 module_param(rcu_kick_kthreads, bool, 0644);
 
 /*
@@ -2180,10 +2210,6 @@ static int __noreturn rcu_gp_kthread(void *arg)
                /* Handle quiescent-state forcing. */
                first_gp_fqs = true;
                j = jiffies_till_first_fqs;
-               if (j > HZ) {
-                       j = HZ;
-                       jiffies_till_first_fqs = HZ;
-               }
                ret = 0;
                for (;;) {
                        if (!ret) {
@@ -2218,13 +2244,6 @@ static int __noreturn rcu_gp_kthread(void *arg)
                                WRITE_ONCE(rsp->gp_activity, jiffies);
                                ret = 0; /* Force full wait till next FQS. */
                                j = jiffies_till_next_fqs;
-                               if (j > HZ) {
-                                       j = HZ;
-                                       jiffies_till_next_fqs = HZ;
-                               } else if (j < 1) {
-                                       j = 1;
-                                       jiffies_till_next_fqs = 1;
-                               }
                        } else {
                                /* Deal with stray signal. */
                                cond_resched_tasks_rcu_qs();