rcu: Export RCU_FAST_NO_HZ parameters to sysfs

RCU_FAST_NO_HZ operation is controlled by four compile-time C-preprocessor
macros, but some use cases benefit greatly from runtime adjustment,
particularly when tuning devices.  This commit therefore creates the
corresponding sysfs entries.

Reported-by: Robin Randhawa <robin.randhawa@arm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index c0164441ab922d7707db3e5423efad01a4dfe16f..28185ad18df38600ad6798f5ffee4dfe086e6c15 100644 (file)
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -1617,6 +1617,15 @@ static void rcu_idle_count_callbacks_posted(void)
 #define RCU_IDLE_GP_DELAY 4            /* Roughly one grace period. */
 #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ)        /* Roughly six seconds. */
 
+static int rcu_idle_flushes = RCU_IDLE_FLUSHES;
+module_param(rcu_idle_flushes, int, 0644);
+static int rcu_idle_opt_flushes = RCU_IDLE_OPT_FLUSHES;
+module_param(rcu_idle_opt_flushes, int, 0644);
+static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
+module_param(rcu_idle_gp_delay, int, 0644);
+static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
+module_param(rcu_idle_lazy_gp_delay, int, 0644);
+
 extern int tick_nohz_enabled;
 
 /*
@@ -1696,10 +1705,10 @@ int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
        }
        /* Set up for the possibility that RCU will post a timer. */
        if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
-               *delta_jiffies = round_up(RCU_IDLE_GP_DELAY + jiffies,
-                                         RCU_IDLE_GP_DELAY) - jiffies;
+               *delta_jiffies = round_up(rcu_idle_gp_delay + jiffies,
+                                         rcu_idle_gp_delay) - jiffies;
        } else {
-               *delta_jiffies = jiffies + RCU_IDLE_LAZY_GP_DELAY;
+               *delta_jiffies = jiffies + rcu_idle_lazy_gp_delay;
                *delta_jiffies = round_jiffies(*delta_jiffies) - jiffies;
        }
        return 0;
@@ -1805,11 +1814,11 @@ static void rcu_prepare_for_idle(int cpu)
                if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
                        trace_rcu_prep_idle("User dyntick with callbacks");
                        rdtp->idle_gp_timer_expires =
-                               round_up(jiffies + RCU_IDLE_GP_DELAY,
-                                        RCU_IDLE_GP_DELAY);
+                               round_up(jiffies + rcu_idle_gp_delay,
+                                        rcu_idle_gp_delay);
                } else if (rcu_cpu_has_callbacks(cpu)) {
                        rdtp->idle_gp_timer_expires =
-                               round_jiffies(jiffies + RCU_IDLE_LAZY_GP_DELAY);
+                               round_jiffies(jiffies + rcu_idle_lazy_gp_delay);
                        trace_rcu_prep_idle("User dyntick with lazy callbacks");
                } else {
                        return;
@@ -1861,8 +1870,8 @@ static void rcu_prepare_for_idle(int cpu)
        /* Check and update the ->dyntick_drain sequencing. */
        if (rdtp->dyntick_drain <= 0) {
                /* First time through, initialize the counter. */
-               rdtp->dyntick_drain = RCU_IDLE_FLUSHES;
-       } else if (rdtp->dyntick_drain <= RCU_IDLE_OPT_FLUSHES &&
+               rdtp->dyntick_drain = rcu_idle_flushes;
+       } else if (rdtp->dyntick_drain <= rcu_idle_opt_flushes &&
                   !rcu_pending(cpu) &&
                   !local_softirq_pending()) {
                /* Can we go dyntick-idle despite still having callbacks? */
@@ -1871,11 +1880,11 @@ static void rcu_prepare_for_idle(int cpu)
                if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
                        trace_rcu_prep_idle("Dyntick with callbacks");
                        rdtp->idle_gp_timer_expires =
-                               round_up(jiffies + RCU_IDLE_GP_DELAY,
-                                        RCU_IDLE_GP_DELAY);
+                               round_up(jiffies + rcu_idle_gp_delay,
+                                        rcu_idle_gp_delay);
                } else {
                        rdtp->idle_gp_timer_expires =
-                               round_jiffies(jiffies + RCU_IDLE_LAZY_GP_DELAY);
+                               round_jiffies(jiffies + rcu_idle_lazy_gp_delay);
                        trace_rcu_prep_idle("Dyntick with lazy callbacks");
                }
                tp = &rdtp->idle_gp_timer;