rcu: simplify the usage of percpu data

&percpu_data is compatible with allocated percpu data.

And we use it and remove the "->rda[NR_CPUS]" array, saving significant
storage on systems with large numbers of CPUs.  This does add an additional
level of indirection and thus an additional cache line referenced, but
because ->rda is not used on the read side, this is OK.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Reviewed-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

4 files changed, 19 insertions, 31 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index d5bc43976c5a..5b1c3c231bae 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -712,7 +712,7 @@ static void
 rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
         __releases(rcu_get_root(rsp)->lock)
 {
-        struct rcu_data *rdp = rsp->rda[smp_processor_id()];
+        struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
         struct rcu_node *rnp = rcu_get_root(rsp);
 
         if (!cpu_needs_another_gp(rsp, rdp) || rsp->fqs_active) {
@@ -960,7 +960,7 @@ rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
 static void rcu_send_cbs_to_orphanage(struct rcu_state *rsp)
 {
         int i;
-        struct rcu_data *rdp = rsp->rda[smp_processor_id()];
+        struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
 
         if (rdp->nxtlist == NULL)
                 return;  /* irqs disabled, so comparison is stable. */
@@ -984,7 +984,7 @@ static void rcu_adopt_orphan_cbs(struct rcu_state *rsp)
         struct rcu_data *rdp;
 
         raw_spin_lock_irqsave(&rsp->onofflock, flags);
-        rdp = rsp->rda[smp_processor_id()];
+        rdp = this_cpu_ptr(rsp->rda);
         if (rsp->orphan_cbs_list == NULL) {
                 raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
                 return;
@@ -1007,7 +1007,7 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
         unsigned long flags;
         unsigned long mask;
         int need_report = 0;
-        struct rcu_data *rdp = rsp->rda[cpu];
+        struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
         struct rcu_node *rnp;
 
         /* Exclude any attempts to start a new grace period. */
@@ -1226,7 +1226,8 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *))
                 cpu = rnp->grplo;
                 bit = 1;
                 for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
-                        if ((rnp->qsmask & bit) != 0 && f(rsp->rda[cpu]))
+                        if ((rnp->qsmask & bit) != 0 &&
+                            f(per_cpu_ptr(rsp->rda, cpu)))
                                 mask |= bit;
                 }
                 if (mask != 0) {
@@ -1402,7 +1403,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
          * a quiescent state betweentimes.
          */
         local_irq_save(flags);
-        rdp = rsp->rda[smp_processor_id()];
+        rdp = this_cpu_ptr(rsp->rda);
         rcu_process_gp_end(rsp, rdp);
         check_for_new_grace_period(rsp, rdp);
 
@@ -1701,7 +1702,7 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
 {
         unsigned long flags;
         int i;
-        struct rcu_data *rdp = rsp->rda[cpu];
+        struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
         struct rcu_node *rnp = rcu_get_root(rsp);
 
         /* Set up local state, ensuring consistent view of global state. */
@@ -1729,7 +1730,7 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptable)
 {
         unsigned long flags;
         unsigned long mask;
-        struct rcu_data *rdp = rsp->rda[cpu];
+        struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
         struct rcu_node *rnp = rcu_get_root(rsp);
 
         /* Set up local state, ensuring consistent view of global state. */
@@ -1865,7 +1866,8 @@ static void __init rcu_init_levelspread(struct rcu_state *rsp)
 /*
  * Helper function for rcu_init() that initializes one rcu_state structure.
  */
-static void __init rcu_init_one(struct rcu_state *rsp)
+static void __init rcu_init_one(struct rcu_state *rsp,
+                struct rcu_data __percpu *rda)
 {
         static char *buf[] = { "rcu_node_level_0",
                                "rcu_node_level_1",
@@ -1918,37 +1920,23 @@ static void __init rcu_init_one(struct rcu_state *rsp)
                 }
         }
 
+        rsp->rda = rda;
         rnp = rsp->level[NUM_RCU_LVLS - 1];
         for_each_possible_cpu(i) {
                 while (i > rnp->grphi)
                         rnp++;
-                rsp->rda[i]->mynode = rnp;
+                per_cpu_ptr(rsp->rda, i)->mynode = rnp;
                 rcu_boot_init_percpu_data(i, rsp);
         }
 }
 
-/*
- * Helper macro for __rcu_init() and __rcu_init_preempt().  To be used
- * nowhere else!  Assigns leaf node pointers into each CPU's rcu_data
- * structure.
- */
-#define RCU_INIT_FLAVOR(rsp, rcu_data) \
-do { \
-        int i; \
-        \
-        for_each_possible_cpu(i) { \
-                (rsp)->rda[i] = &per_cpu(rcu_data, i); \
-        } \
-        rcu_init_one(rsp); \
-} while (0)
-
 void __init rcu_init(void)
 {
         int cpu;
 
         rcu_bootup_announce();
-        RCU_INIT_FLAVOR(&rcu_sched_state, rcu_sched_data);
-        RCU_INIT_FLAVOR(&rcu_bh_state, rcu_bh_data);
+        rcu_init_one(&rcu_sched_state, &rcu_sched_data);
+        rcu_init_one(&rcu_bh_state, &rcu_bh_data);
         __rcu_init_preempt();
         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
 
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 14c040b18ed0..5ce197e87792 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -283,7 +283,7 @@ struct rcu_state {
         struct rcu_node *level[NUM_RCU_LVLS];   /* Hierarchy levels. */
         u32 levelcnt[MAX_RCU_LVLS + 1];         /* # nodes in each level. */
         u8 levelspread[NUM_RCU_LVLS];           /* kids/node in each level. */
-        struct rcu_data *rda[NR_CPUS];          /* array of rdp pointers. */
+        struct rcu_data __percpu *rda;          /* pointer of percu rcu_data. */
 
         /* The following fields are guarded by the root rcu_node's lock. */
 
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 0e4f420245d9..9906f85c7780 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -154,7 +154,7 @@ static void rcu_preempt_note_context_switch(int cpu)
             (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
 
                 /* Possibly blocking in an RCU read-side critical section. */
-                rdp = rcu_preempt_state.rda[cpu];
+                rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
                 rnp = rdp->mynode;
                 raw_spin_lock_irqsave(&rnp->lock, flags);
                 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
@@ -771,7 +771,7 @@ static void rcu_preempt_send_cbs_to_orphanage(void)
  */
 static void __init __rcu_init_preempt(void)
 {
-        RCU_INIT_FLAVOR(&rcu_preempt_state, rcu_preempt_data);
+        rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
 }
 
 /*
diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c
index 36c95b45738e..458e032a3a30 100644
--- a/kernel/rcutree_trace.c
+++ b/kernel/rcutree_trace.c
@@ -262,7 +262,7 @@ static void print_rcu_pendings(struct seq_file *m, struct rcu_state *rsp)
         struct rcu_data *rdp;
 
         for_each_possible_cpu(cpu) {
-                rdp = rsp->rda[cpu];
+                rdp = per_cpu_ptr(rsp->rda, cpu);
                 if (rdp->beenonline)
                         print_one_rcu_pending(m, rdp);
         }