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: Ingo Molnar <mingo@kernel.org>

9 files changed, 72 insertions, 51 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 82365dde00a8..4865e9bfd08d 100644
--- a/Documentation/kernel-parameters.txt
+++ b/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.
 
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index b758ce17b309..8e0948c872fc 100644
--- a/include/linux/rcupdate.h
+++ b/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 */
diff --git a/include/linux/tick.h b/include/linux/tick.h
index b4e3b0c9639e..0b6873cbf512 100644
--- a/include/linux/tick.h
+++ b/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
 
diff --git a/init/main.c b/init/main.c
index 63534a141b4e..2acb5bbde99b 100644
--- a/init/main.c
+++ b/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();
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index f5ab50235cba..1d4ceff793a4 100644
--- a/kernel/rcutree.c
+++ b/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);
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index f993c0ac47db..38acc49da2c6 100644
--- a/kernel/rcutree.h
+++ b/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,
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index a5745e9b5d5a..0cd91cc18db4 100644
--- a/kernel/rcutree_plugin.h
+++ b/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)
 {
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index 358d601a4fec..99c3f13dd478 100644
--- a/kernel/time/Kconfig
+++ b/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
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 369b5769fc97..a76e09044f9f 100644
--- a/kernel/time/tick-sched.c
+++ b/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
-                have_nohz_full_mask = true;
+                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);
-                cpumask_clear_cpu(cpu, nohz_full_mask);
-                preempt_enable();
+        /* 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);
+                }
         }
-        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