rcu: use softirq instead of kthreads except when RCU_BOOST=y

This patch #ifdefs RCU kthreads out of the kernel unless RCU_BOOST=y,
thus eliminating context-switch overhead if RCU priority boosting has
not been configured.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 23 insertions, 9 deletions

diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c
index 9678cc3650f5..4e144876dc68 100644
--- a/kernel/rcutree_trace.c
+++ b/kernel/rcutree_trace.c
@@ -46,6 +46,8 @@
 #define RCU_TREE_NONCORE
 #include "rcutree.h"
 
+#ifdef CONFIG_RCU_BOOST
+
 DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
 DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_cpu);
 DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
@@ -58,6 +60,8 @@ static char convert_kthread_status(unsigned int kthread_status)
         return "SRWOY"[kthread_status];
 }
 
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
 static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
 {
         if (!rdp->beenonline)
@@ -76,7 +80,7 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
                    rdp->dynticks_fqs);
 #endif /* #ifdef CONFIG_NO_HZ */
         seq_printf(m, " of=%lu ri=%lu", rdp->offline_fqs, rdp->resched_ipi);
-        seq_printf(m, " ql=%ld qs=%c%c%c%c kt=%d/%c/%d ktl=%x b=%ld",
+        seq_printf(m, " ql=%ld qs=%c%c%c%c",
                    rdp->qlen,
                    ".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] !=
                         rdp->nxttail[RCU_NEXT_TAIL]],
@@ -84,13 +88,16 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
                         rdp->nxttail[RCU_NEXT_READY_TAIL]],
                    ".W"[rdp->nxttail[RCU_DONE_TAIL] !=
                         rdp->nxttail[RCU_WAIT_TAIL]],
-                   ".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]],
+                   ".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]]);
+#ifdef CONFIG_RCU_BOOST
+        seq_printf(m, " kt=%d/%c/%d ktl=%x",
                    per_cpu(rcu_cpu_has_work, rdp->cpu),
                    convert_kthread_status(per_cpu(rcu_cpu_kthread_status,
                                           rdp->cpu)),
                    per_cpu(rcu_cpu_kthread_cpu, rdp->cpu),
-                   per_cpu(rcu_cpu_kthread_loops, rdp->cpu) & 0xffff,
-                   rdp->blimit);
+                   per_cpu(rcu_cpu_kthread_loops, rdp->cpu) & 0xffff);
+#endif /* #ifdef CONFIG_RCU_BOOST */
+        seq_printf(m, " b=%ld", rdp->blimit);
         seq_printf(m, " ci=%lu co=%lu ca=%lu\n",
                    rdp->n_cbs_invoked, rdp->n_cbs_orphaned, rdp->n_cbs_adopted);
 }
@@ -147,18 +154,21 @@ static void print_one_rcu_data_csv(struct seq_file *m, struct rcu_data *rdp)
                    rdp->dynticks_fqs);
 #endif /* #ifdef CONFIG_NO_HZ */
         seq_printf(m, ",%lu,%lu", rdp->offline_fqs, rdp->resched_ipi);
-        seq_printf(m, ",%ld,\"%c%c%c%c\",%d,\"%c\",%ld", rdp->qlen,
+        seq_printf(m, ",%ld,\"%c%c%c%c\"", rdp->qlen,
                    ".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] !=
                         rdp->nxttail[RCU_NEXT_TAIL]],
                    ".R"[rdp->nxttail[RCU_WAIT_TAIL] !=
                         rdp->nxttail[RCU_NEXT_READY_TAIL]],
                    ".W"[rdp->nxttail[RCU_DONE_TAIL] !=
                         rdp->nxttail[RCU_WAIT_TAIL]],
-                   ".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]],
+                   ".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]]);
+#ifdef CONFIG_RCU_BOOST
+        seq_printf(m, ",%d,\"%c\"",
                    per_cpu(rcu_cpu_has_work, rdp->cpu),
                    convert_kthread_status(per_cpu(rcu_cpu_kthread_status,
-                                          rdp->cpu)),
-                   rdp->blimit);
+                                          rdp->cpu)));
+#endif /* #ifdef CONFIG_RCU_BOOST */
+        seq_printf(m, ",%ld", rdp->blimit);
         seq_printf(m, ",%lu,%lu,%lu\n",
                    rdp->n_cbs_invoked, rdp->n_cbs_orphaned, rdp->n_cbs_adopted);
 }
@@ -169,7 +179,11 @@ static int show_rcudata_csv(struct seq_file *m, void *unused)
 #ifdef CONFIG_NO_HZ
         seq_puts(m, "\"dt\",\"dt nesting\",\"dt NMI nesting\",\"df\",");
 #endif /* #ifdef CONFIG_NO_HZ */
-        seq_puts(m, "\"of\",\"ri\",\"ql\",\"b\",\"ci\",\"co\",\"ca\"\n");
+        seq_puts(m, "\"of\",\"ri\",\"ql\",\"qs\"");
+#ifdef CONFIG_RCU_BOOST
+        seq_puts(m, "\"kt\",\"ktl\"");
+#endif /* #ifdef CONFIG_RCU_BOOST */
+        seq_puts(m, ",\"b\",\"ci\",\"co\",\"ca\"\n");
 #ifdef CONFIG_TREE_PREEMPT_RCU
         seq_puts(m, "\"rcu_preempt:\"\n");
         PRINT_RCU_DATA(rcu_preempt_data, print_one_rcu_data_csv, m);