rcu: Optimize rcu_needs_cpu() for RCU_NOCB_CPU_ALL

If CONFIG_RCU_NOCB_CPU_ALL=y, then rcu_needs_cpu() will always
return false, however, the current version nevertheless checks
for RCU callbacks.  This commit therefore creates a static inline
implementation of rcu_needs_cpu() that unconditionally returns false
when CONFIG_RCU_NOCB_CPU_ALL=y.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 281c90f8989e6c06734527763a1f266d6a1f6f0d..5f7d5f410d50e79405c2d5e6c5c0d5d8a211547b 100644 (file)
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -1015,6 +1015,14 @@ 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))
 
+#if defined(CONFIG_TINY_RCU) || defined(CONFIG_RCU_NOCB_CPU_ALL)
+static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
+{
+       *delta_jiffies = ULONG_MAX;
+       return 0;
+}
+#endif /* #if defined(CONFIG_TINY_RCU) || defined(CONFIG_RCU_NOCB_CPU_ALL) */
+
 #if defined(CONFIG_RCU_NOCB_CPU_ALL)
 static inline bool rcu_is_nocb_cpu(int cpu) { return true; }
 #elif defined(CONFIG_RCU_NOCB_CPU)

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 6f01771b571c00eede5aaae145fdcf7382e61cd9..9524903487d074702ec08409dcfc6b7ea2682bfc 100644 (file)
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -68,12 +68,6 @@ static inline void kfree_call_rcu(struct rcu_head *head,
        call_rcu(head, func);
 }
 
-static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
-{
-       *delta_jiffies = ULONG_MAX;
-       return 0;
-}
-
 static inline void rcu_note_context_switch(int cpu)
 {
        rcu_sched_qs(cpu);

diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 72137ee8c603b2c0c45ea7f729211e12cfad3941..81198c84e268581058ce3d968f2587a42039c20a 100644 (file)
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -31,7 +31,9 @@
 #define __LINUX_RCUTREE_H
 
 void rcu_note_context_switch(int cpu);
+#ifndef CONFIG_RCU_NOCB_CPU_ALL
 int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies);
+#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
 void rcu_cpu_stall_reset(void);
 
 /*

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index b3d116cd072d7bd24803a52c8d6b478930bd6b8b..c2c8234a02916cacd8efbf112623a4a40f33688a 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2880,7 +2880,7 @@ static int rcu_pending(int cpu)
  * non-NULL, store an indication of whether all callbacks are lazy.
  * (If there are no callbacks, all of them are deemed to be lazy.)
  */
-static int rcu_cpu_has_callbacks(int cpu, bool *all_lazy)
+static int __maybe_unused rcu_cpu_has_callbacks(int cpu, bool *all_lazy)
 {
        bool al = true;
        bool hc = false;

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 39a50b918bffbc2fc79c30f4332ca3f133ba8919..820b06aefbee335b0b7913b850422747e1ce4ce9 100644 (file)
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1586,11 +1586,13 @@ static void rcu_prepare_kthreads(int cpu)
  * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
  * any flavor of RCU.
  */
+#ifndef CONFIG_RCU_NOCB_CPU_ALL
 int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
 {
        *delta_jiffies = ULONG_MAX;
        return rcu_cpu_has_callbacks(cpu, NULL);
 }
+#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
 
 /*
  * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
@@ -1696,6 +1698,7 @@ static bool rcu_try_advance_all_cbs(void)
  *
  * The caller must have disabled interrupts.
  */
+#ifndef CONFIG_RCU_NOCB_CPU_ALL
 int rcu_needs_cpu(int cpu, unsigned long *dj)
 {
        struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
@@ -1726,6 +1729,7 @@ int rcu_needs_cpu(int cpu, unsigned long *dj)
        }
        return 0;
 }
+#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
 
 /*
  * Prepare a CPU for idle from an RCU perspective.  The first major task