rcu: Optimize the 'rcu_pending' for RCU trace

This patch implements the new 'rcu_pending' interface under each rsp
directory, by using the 'CPU units sequence reading', thus avoiding loss
of tracing data.

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

1 files changed, 35 insertions, 6 deletions

diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c
index e387a642632b..8b2486722211 100644
--- a/kernel/rcutree_trace.c
+++ b/kernel/rcutree_trace.c
@@ -467,6 +467,8 @@ static const struct file_operations rcugp_fops = {
 
 static void print_one_rcu_pending(struct seq_file *m, struct rcu_data *rdp)
 {
+        if (!rdp->beenonline)
+                return;
         seq_printf(m, "%3d%cnp=%ld ",
                    rdp->cpu,
                    cpu_is_offline(rdp->cpu) ? '!' : ' ',
@@ -485,16 +487,12 @@ static void print_one_rcu_pending(struct seq_file *m, struct rcu_data *rdp)
 static int show_rcu_pending(struct seq_file *m, void *unused)
 {
         int cpu;
-        struct rcu_data *rdp;
         struct rcu_state *rsp;
 
         for_each_rcu_flavor(rsp) {
                 seq_printf(m, "%s:\n", rsp->name);
-                for_each_possible_cpu(cpu) {
-                        rdp = per_cpu_ptr(rsp->rda, cpu);
-                        if (rdp->beenonline)
-                                print_one_rcu_pending(m, rdp);
-                }
+                for_each_possible_cpu(cpu)
+                        print_one_rcu_pending(m, per_cpu_ptr(rsp->rda, cpu));
         }
         return 0;
 }
@@ -512,6 +510,32 @@ static const struct file_operations rcu_pending_fops = {
         .release = single_release,
 };
 
+static int new_show_rcu_pending(struct seq_file *m, void *v)
+{
+        print_one_rcu_pending(m, (struct rcu_data *)v);
+        return 0;
+}
+
+static const struct seq_operations new_rcu_pending_op = {
+        .start = r_start,
+        .next  = r_next,
+        .stop  = r_stop,
+        .show  = new_show_rcu_pending,
+};
+
+static int new_rcu_pending_open(struct inode *inode, struct file *file)
+{
+        return r_open(inode, file, &new_rcu_pending_op);
+}
+
+static const struct file_operations new_rcu_pending_fops = {
+        .owner = THIS_MODULE,
+        .open = new_rcu_pending_open,
+        .read = seq_read,
+        .llseek = no_llseek,
+        .release = seq_release,
+};
+
 static int show_rcutorture(struct seq_file *m, void *unused)
 {
         seq_printf(m, "rcutorture test sequence: %lu %s\n",
@@ -561,6 +585,11 @@ static int __init rcutree_trace_init(void)
                                         rspdir, rsp, &new_rcudata_csv_fops);
                         if (!retval)
                                 goto free_out;
+
+                        retval = debugfs_create_file("rcu_pending", 0444,
+                                        rspdir, rsp, &new_rcu_pending_fops);
+                        if (!retval)
+                                goto free_out;
         }
 
         retval = debugfs_create_file("rcubarrier", 0444, rcudir,