Merge branch 'timers/nohz-reviewed' of...

Merge branch 'timers/nohz-reviewed' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks into timers/nohz

Pull full dynticks timekeeping and RCU improvements from Frederic Weisbecker.
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Documentation/kernel-parameters.txt

@@ -1916,8 +1916,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 	nohz_full=	[KNL,BOOT]
 			In kernels built with CONFIG_NO_HZ_FULL=y, set
 			the specified list of CPUs whose tick will be stopped
-			whenever possible. You need to keep at least one online
-			CPU outside the range to maintain the timekeeping.
+			whenever possible. The boot CPU will be forced outside
+			the range to maintain the timekeeping.
+			The CPUs in this range must also be included in the
+			rcu_nocbs= set.
 
 	noiotrap	[SH] Disables trapped I/O port accesses.
 

include/linux/rcupdate.h

@@ -999,4 +999,11 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
 #define kfree_rcu(ptr, rcu_head)					\
 	__kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
 
+#ifdef CONFIG_RCU_NOCB_CPU
+extern bool rcu_is_nocb_cpu(int cpu);
+#else
+static inline bool rcu_is_nocb_cpu(int cpu) { return false; }
+#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
+
+
 #endif /* __LINUX_RCUPDATE_H */

include/linux/tick.h

@@ -158,8 +158,10 @@ static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; }
 # endif /* !CONFIG_NO_HZ_COMMON */
 
 #ifdef CONFIG_NO_HZ_FULL
+extern void tick_nohz_init(void);
 extern int tick_nohz_full_cpu(int cpu);
 #else
+static inline void tick_nohz_init(void) { }
 static inline int tick_nohz_full_cpu(int cpu) { return 0; }
 #endif
 

init/main.c

@@ -547,6 +547,7 @@ asmlinkage void __init start_kernel(void)
 	idr_init_cache();
 	perf_event_init();
 	rcu_init();
+	tick_nohz_init();
 	radix_tree_init();
 	/* init some links before init_ISA_irqs() */
 	early_irq_init();

kernel/rcutree.c

@@ -1695,7 +1695,7 @@ rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
 			  struct rcu_node *rnp, struct rcu_data *rdp)
 {
 	/* No-CBs CPUs do not have orphanable callbacks. */
-	if (is_nocb_cpu(rdp->cpu))
+	if (rcu_is_nocb_cpu(rdp->cpu))
 		return;
 
 	/*
@@ -2757,10 +2757,10 @@ static void _rcu_barrier(struct rcu_state *rsp)
 	 * corresponding CPU's preceding callbacks have been invoked.
 	 */
 	for_each_possible_cpu(cpu) {
-		if (!cpu_online(cpu) && !is_nocb_cpu(cpu))
+		if (!cpu_online(cpu) && !rcu_is_nocb_cpu(cpu))
 			continue;
 		rdp = per_cpu_ptr(rsp->rda, cpu);
-		if (is_nocb_cpu(cpu)) {
+		if (rcu_is_nocb_cpu(cpu)) {
 			_rcu_barrier_trace(rsp, "OnlineNoCB", cpu,
 					   rsp->n_barrier_done);
 			atomic_inc(&rsp->barrier_cpu_count);

kernel/rcutree.h

@@ -529,7 +529,6 @@ static void print_cpu_stall_info(struct rcu_state *rsp, int cpu);
 static void print_cpu_stall_info_end(void);
 static void zero_cpu_stall_ticks(struct rcu_data *rdp);
 static void increment_cpu_stall_ticks(void);
-static bool is_nocb_cpu(int cpu);
 static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
 			    bool lazy);
 static bool rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,

kernel/rcutree_plugin.h

@@ -2167,7 +2167,7 @@ static int __init parse_rcu_nocb_poll(char *arg)
 early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
 
 /* Is the specified CPU a no-CPUs CPU? */
-static bool is_nocb_cpu(int cpu)
+bool rcu_is_nocb_cpu(int cpu)
 {
 	if (have_rcu_nocb_mask)
 		return cpumask_test_cpu(cpu, rcu_nocb_mask);
@@ -2225,7 +2225,7 @@ static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
 			    bool lazy)
 {
 
-	if (!is_nocb_cpu(rdp->cpu))
+	if (!rcu_is_nocb_cpu(rdp->cpu))
 		return 0;
 	__call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy);
 	return 1;
@@ -2242,7 +2242,7 @@ static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
 	long qll = rsp->qlen_lazy;
 
 	/* If this is not a no-CBs CPU, tell the caller to do it the old way. */
-	if (!is_nocb_cpu(smp_processor_id()))
+	if (!rcu_is_nocb_cpu(smp_processor_id()))
 		return 0;
 	rsp->qlen = 0;
 	rsp->qlen_lazy = 0;
@@ -2282,7 +2282,7 @@ static bool nocb_cpu_expendable(int cpu)
 	 * If there are no no-CB CPUs or if this CPU is not a no-CB CPU,
 	 * then offlining this CPU is harmless.  Let it happen.
 	 */
-	if (!have_rcu_nocb_mask || is_nocb_cpu(cpu))
+	if (!have_rcu_nocb_mask || rcu_is_nocb_cpu(cpu))
 		return 1;
 
 	/* If no memory, play it safe and keep the CPU around. */
@@ -2464,11 +2464,6 @@ static void __init rcu_init_nocb(void)
 
 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
 
-static bool is_nocb_cpu(int cpu)
-{
-	return false;
-}
-
 static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
 			    bool lazy)
 {

kernel/time/Kconfig

@@ -128,6 +128,16 @@ config NO_HZ_FULL
 
 endchoice
 
+config NO_HZ_FULL_ALL
+       bool "Full dynticks system on all CPUs by default"
+       depends on NO_HZ_FULL
+       help
+         If the user doesn't pass the nohz_full boot option to
+	 define the range of full dynticks CPUs, consider that all
+	 CPUs in the system are full dynticks by default.
+	 Note the boot CPU will still be kept outside the range to
+	 handle the timekeeping duty.
+
 config NO_HZ
 	bool "Old Idle dynticks config"
 	depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS

kernel/time/tick-sched.c

@@ -158,11 +158,21 @@ int tick_nohz_full_cpu(int cpu)
 /* Parse the boot-time nohz CPU list from the kernel parameters. */
 static int __init tick_nohz_full_setup(char *str)
 {
+	int cpu;
+
 	alloc_bootmem_cpumask_var(&nohz_full_mask);
-	if (cpulist_parse(str, nohz_full_mask) < 0)
+	if (cpulist_parse(str, nohz_full_mask) < 0) {
 		pr_warning("NOHZ: Incorrect nohz_full cpumask\n");
-	else
+		return 1;
+	}
+
+	cpu = smp_processor_id();
+	if (cpumask_test_cpu(cpu, nohz_full_mask)) {
+		pr_warning("NO_HZ: Clearing %d from nohz_full range for timekeeping\n", cpu);
+		cpumask_clear_cpu(cpu, nohz_full_mask);
+	}
 	have_nohz_full_mask = true;
+
 	return 1;
 }
 __setup("nohz_full=", tick_nohz_full_setup);
@@ -193,51 +203,46 @@ static int __cpuinit tick_nohz_cpu_down_callback(struct notifier_block *nfb,
  */
 static char __initdata nohz_full_buf[NR_CPUS + 1];
 
-static int __init init_tick_nohz_full(void)
+static int tick_nohz_init_all(void)
 {
-	cpumask_var_t online_nohz;
-	int cpu;
+	int err = -1;
 
-	if (!have_nohz_full_mask)
-		return 0;
+#ifdef CONFIG_NO_HZ_FULL_ALL
+	if (!alloc_cpumask_var(&nohz_full_mask, GFP_KERNEL)) {
+		pr_err("NO_HZ: Can't allocate full dynticks cpumask\n");
+		return err;
+	}
+	err = 0;
+	cpumask_setall(nohz_full_mask);
+	cpumask_clear_cpu(smp_processor_id(), nohz_full_mask);
+	have_nohz_full_mask = true;
+#endif
+	return err;
+}
 
-	cpu_notifier(tick_nohz_cpu_down_callback, 0);
+void __init tick_nohz_init(void)
+{
+	int cpu;
 
-	if (!zalloc_cpumask_var(&online_nohz, GFP_KERNEL)) {
-		pr_warning("NO_HZ: Not enough memory to check full nohz mask\n");
-		return -ENOMEM;
+	if (!have_nohz_full_mask) {
+		if (tick_nohz_init_all() < 0)
+			return;
 	}
 
-	/*
-	 * CPUs can probably not be concurrently offlined on initcall time.
-	 * But we are paranoid, aren't we?
-	 */
-	get_online_cpus();
+	cpu_notifier(tick_nohz_cpu_down_callback, 0);
 
-	/* Ensure we keep a CPU outside the dynticks range for timekeeping */
-	cpumask_and(online_nohz, cpu_online_mask, nohz_full_mask);
-	if (cpumask_equal(online_nohz, cpu_online_mask)) {
-		pr_warning("NO_HZ: Must keep at least one online CPU "
-			   "out of nohz_full range\n");
-		/*
-		 * We know the current CPU doesn't have its tick stopped.
-		 * Let's use it for the timekeeping duty.
-		 */
-		preempt_disable();
-		cpu = smp_processor_id();
-		pr_warning("NO_HZ: Clearing %d from nohz_full range\n", cpu);
+	/* Make sure full dynticks CPU are also RCU nocbs */
+	for_each_cpu(cpu, nohz_full_mask) {
+		if (!rcu_is_nocb_cpu(cpu)) {
+			pr_warning("NO_HZ: CPU %d is not RCU nocb: "
+				   "cleared from nohz_full range", cpu);
 			cpumask_clear_cpu(cpu, nohz_full_mask);
-		preempt_enable();
 		}
-	put_online_cpus();
-	free_cpumask_var(online_nohz);
+	}
 
 	cpulist_scnprintf(nohz_full_buf, sizeof(nohz_full_buf), nohz_full_mask);
 	pr_info("NO_HZ: Full dynticks CPUs: %s.\n", nohz_full_buf);
-
-	return 0;
 }
-core_initcall(init_tick_nohz_full);
 #else
 #define have_nohz_full_mask (0)
 #endif