rcu: Add __rcu_pending tracing to hierarchical RCU

Add tracing to __rcu_pending() to provide information on why RCU processing was kicked off. This is helpful for debugging hierarchical RCU, and might also be helpful in learning how hierarchical RCU operates. Located-by: Anton Blanchard <anton@au1.ibm.com> Tested-by: Anton Blanchard <anton@au1.ibm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: anton@samba.org Cc: akpm@linux-foundation.org Cc: dipankar@in.ibm.com Cc: manfred@colorfullife.com Cc: cl@linux-foundation.org Cc: josht@linux.vnet.ibm.com Cc: schamp@sgi.com Cc: niv@us.ibm.com Cc: dvhltc@us.ibm.com Cc: ego@in.ibm.com Cc: laijs@cn.fujitsu.com Cc: rostedt@goodmis.org Cc: peterz@infradead.org Cc: penberg@cs.helsinki.fi Cc: andi@firstfloor.org Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> LKML-Reference: <1239683479943-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>

rcu: Add __rcu_pending tracing to hierarchical RCU
Add tracing to __rcu_pending() to provide information on why RCU processing was kicked off. This is helpful for debugging hierarchical RCU, and might also be helpful in learning how hierarchical RCU operates. Located-by: Anton Blanchard <anton@au1.ibm.com> Tested-by: Anton Blanchard <anton@au1.ibm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: anton@samba.org Cc: akpm@linux-foundation.org Cc: dipankar@in.ibm.com Cc: manfred@colorfullife.com Cc: cl@linux-foundation.org Cc: josht@linux.vnet.ibm.com Cc: schamp@sgi.com Cc: niv@us.ibm.com Cc: dvhltc@us.ibm.com Cc: ego@in.ibm.com Cc: laijs@cn.fujitsu.com Cc: rostedt@goodmis.org Cc: peterz@infradead.org Cc: penberg@cs.helsinki.fi Cc: andi@firstfloor.org Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> LKML-Reference: <1239683479943-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Paul E. McKenney · Ingo Molnar
1 parent 05cfbd66d0
Showing 3 changed files with 90 additions and 8 deletions Side-by-side Diff
include/linux/rcutree.h
kernel/rcutree.c
kernel/rcutree_trace.c
@@ -161,8 +161,15 @@
 	unsigned long offline_fqs;	/* Kicked due to being offline. */
 	unsigned long resched_ipi;	/* Sent a resched IPI. */
  
-	/* 5) For future __rcu_pending statistics. */
+	/* 5) __rcu_pending() statistics. */
 	long n_rcu_pending;		/* rcu_pending() calls since boot. */
+	long n_rp_qs_pending;
+	long n_rp_cb_ready;
+	long n_rp_cpu_needs_gp;
+	long n_rp_gp_completed;
+	long n_rp_gp_started;
+	long n_rp_need_fqs;
+	long n_rp_need_nothing;
  
 	int cpu;
 };
@@ -1259,31 +1259,44 @@
 	check_cpu_stall(rsp, rdp);
  
 	/* Is the RCU core waiting for a quiescent state from this CPU? */
-	if (rdp->qs_pending)
+	if (rdp->qs_pending) {
+		rdp->n_rp_qs_pending++;
 		return 1;
+	}
  
 	/* Does this CPU have callbacks ready to invoke? */
-	if (cpu_has_callbacks_ready_to_invoke(rdp))
+	if (cpu_has_callbacks_ready_to_invoke(rdp)) {
+		rdp->n_rp_cb_ready++;
 		return 1;
+	}
  
 	/* Has RCU gone idle with this CPU needing another grace period? */
-	if (cpu_needs_another_gp(rsp, rdp))
+	if (cpu_needs_another_gp(rsp, rdp)) {
+		rdp->n_rp_cpu_needs_gp++;
 		return 1;
+	}
  
 	/* Has another RCU grace period completed?  */
-	if (ACCESS_ONCE(rsp->completed) != rdp->completed) /* outside of lock */
+	if (ACCESS_ONCE(rsp->completed) != rdp->completed) { /* outside lock */
+		rdp->n_rp_gp_completed++;
 		return 1;
+	}
  
 	/* Has a new RCU grace period started? */
-	if (ACCESS_ONCE(rsp->gpnum) != rdp->gpnum) /* outside of lock */
+	if (ACCESS_ONCE(rsp->gpnum) != rdp->gpnum) { /* outside lock */
+		rdp->n_rp_gp_started++;
 		return 1;
+	}
  
 	/* Has an RCU GP gone long enough to send resched IPIs &c? */
 	if (ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum) &&
-	    ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0))
+	    ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0)) {
+		rdp->n_rp_need_fqs++;
 		return 1;
+	}
  
 	/* nothing to do */
+	rdp->n_rp_need_nothing++;
 	return 0;
 }
  
@@ -213,7 +213,63 @@
 	.release = single_release,
 };
  
-static struct dentry *rcudir, *datadir, *datadir_csv, *hierdir, *gpdir;
+static void print_one_rcu_pending(struct seq_file *m, struct rcu_data *rdp)
+{
+	seq_printf(m, "%3d%cnp=%ld "
+		   "qsp=%ld cbr=%ld cng=%ld gpc=%ld gps=%ld nf=%ld nn=%ld\n",
+		   rdp->cpu,
+		   cpu_is_offline(rdp->cpu) ? '!' : ' ',
+		   rdp->n_rcu_pending,
+		   rdp->n_rp_qs_pending,
+		   rdp->n_rp_cb_ready,
+		   rdp->n_rp_cpu_needs_gp,
+		   rdp->n_rp_gp_completed,
+		   rdp->n_rp_gp_started,
+		   rdp->n_rp_need_fqs,
+		   rdp->n_rp_need_nothing);
+}
+
+static void print_rcu_pendings(struct seq_file *m, struct rcu_state *rsp)
+{
+	int cpu;
+	struct rcu_data *rdp;
+
+	for_each_possible_cpu(cpu) {
+		rdp = rsp->rda[cpu];
+		if (rdp->beenonline)
+			print_one_rcu_pending(m, rdp);
+	}
+}
+
+static int show_rcu_pending(struct seq_file *m, void *unused)
+{
+	seq_puts(m, "rcu:\n");
+	print_rcu_pendings(m, &rcu_state);
+	seq_puts(m, "rcu_bh:\n");
+	print_rcu_pendings(m, &rcu_bh_state);
+	return 0;
+}
+
+static int rcu_pending_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, show_rcu_pending, NULL);
+}
+
+static struct file_operations rcu_pending_fops = {
+	.owner = THIS_MODULE,
+	.open = rcu_pending_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = single_release,
+};
+
+static struct dentry *rcudir;
+static struct dentry *datadir;
+static struct dentry *datadir_csv;
+static struct dentry *gpdir;
+static struct dentry *hierdir;
+static struct dentry *rcu_pendingdir;
+
 static int __init rcuclassic_trace_init(void)
 {
 	rcudir = debugfs_create_dir("rcu", NULL);
@@ -238,6 +294,11 @@
 						NULL, &rcuhier_fops);
 	if (!hierdir)
 		goto free_out;
+
+	rcu_pendingdir = debugfs_create_file("rcu_pending", 0444, rcudir,
+						NULL, &rcu_pending_fops);
+	if (!rcu_pendingdir)
+		goto free_out;
 	return 0;
 free_out:
 	if (datadir)
@@ -257,6 +318,7 @@
 	debugfs_remove(datadir_csv);
 	debugfs_remove(gpdir);
 	debugfs_remove(hierdir);
+	debugfs_remove(rcu_pendingdir);
 	debugfs_remove(rcudir);
 }
...	...	@@ -161,8 +161,15 @@
161	161	unsigned long offline_fqs; /* Kicked due to being offline. */
162	162	unsigned long resched_ipi; /* Sent a resched IPI. */
163	163
164		- /* 5) For future __rcu_pending statistics. */
	164	+ /* 5) __rcu_pending() statistics. */
165	165	long n_rcu_pending; /* rcu_pending() calls since boot. */
	166	+ long n_rp_qs_pending;
	167	+ long n_rp_cb_ready;
	168	+ long n_rp_cpu_needs_gp;
	169	+ long n_rp_gp_completed;
	170	+ long n_rp_gp_started;
	171	+ long n_rp_need_fqs;
	172	+ long n_rp_need_nothing;
166	173
167	174	int cpu;
168	175	};
...	...	@@ -1259,31 +1259,44 @@
1259	1259	check_cpu_stall(rsp, rdp);
1260	1260
1261	1261	/* Is the RCU core waiting for a quiescent state from this CPU? */
1262		- if (rdp->qs_pending)
	1262	+ if (rdp->qs_pending) {
	1263	+ rdp->n_rp_qs_pending++;
1263	1264	return 1;
	1265	+ }
1264	1266
1265	1267	/* Does this CPU have callbacks ready to invoke? */
1266		- if (cpu_has_callbacks_ready_to_invoke(rdp))
	1268	+ if (cpu_has_callbacks_ready_to_invoke(rdp)) {
	1269	+ rdp->n_rp_cb_ready++;
1267	1270	return 1;
	1271	+ }
1268	1272
1269	1273	/* Has RCU gone idle with this CPU needing another grace period? */
1270		- if (cpu_needs_another_gp(rsp, rdp))
	1274	+ if (cpu_needs_another_gp(rsp, rdp)) {
	1275	+ rdp->n_rp_cpu_needs_gp++;
1271	1276	return 1;
	1277	+ }
1272	1278
1273	1279	/* Has another RCU grace period completed? */
1274		- if (ACCESS_ONCE(rsp->completed) != rdp->completed) /* outside of lock */
	1280	+ if (ACCESS_ONCE(rsp->completed) != rdp->completed) { /* outside lock */
	1281	+ rdp->n_rp_gp_completed++;
1275	1282	return 1;
	1283	+ }
1276	1284
1277	1285	/* Has a new RCU grace period started? */
1278		- if (ACCESS_ONCE(rsp->gpnum) != rdp->gpnum) /* outside of lock */
	1286	+ if (ACCESS_ONCE(rsp->gpnum) != rdp->gpnum) { /* outside lock */
	1287	+ rdp->n_rp_gp_started++;
1279	1288	return 1;
	1289	+ }
1280	1290
1281	1291	/* Has an RCU GP gone long enough to send resched IPIs &c? */
1282	1292	if (ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum) &&
1283		- ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0))
	1293	+ ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0)) {
	1294	+ rdp->n_rp_need_fqs++;
1284	1295	return 1;
	1296	+ }
1285	1297
1286	1298	/* nothing to do */
	1299	+ rdp->n_rp_need_nothing++;
1287	1300	return 0;
1288	1301	}
1289	1302
...	...	@@ -213,7 +213,63 @@
213	213	.release = single_release,
214	214	};
215	215
216		-static struct dentry rcudir, datadir, datadir_csv, hierdir, *gpdir;
	216	+static void print_one_rcu_pending(struct seq_file m, struct rcu_data rdp)
	217	+{
	218	+ seq_printf(m, "%3d%cnp=%ld "
	219	+ "qsp=%ld cbr=%ld cng=%ld gpc=%ld gps=%ld nf=%ld nn=%ld\n",
	220	+ rdp->cpu,
	221	+ cpu_is_offline(rdp->cpu) ? '!' : ' ',
	222	+ rdp->n_rcu_pending,
	223	+ rdp->n_rp_qs_pending,
	224	+ rdp->n_rp_cb_ready,
	225	+ rdp->n_rp_cpu_needs_gp,
	226	+ rdp->n_rp_gp_completed,
	227	+ rdp->n_rp_gp_started,
	228	+ rdp->n_rp_need_fqs,
	229	+ rdp->n_rp_need_nothing);
	230	+}
	231	+
	232	+static void print_rcu_pendings(struct seq_file m, struct rcu_state rsp)
	233	+{
	234	+ int cpu;
	235	+ struct rcu_data *rdp;
	236	+
	237	+ for_each_possible_cpu(cpu) {
	238	+ rdp = rsp->rda[cpu];
	239	+ if (rdp->beenonline)
	240	+ print_one_rcu_pending(m, rdp);
	241	+ }
	242	+}
	243	+
	244	+static int show_rcu_pending(struct seq_file m, void unused)
	245	+{
	246	+ seq_puts(m, "rcu:\n");
	247	+ print_rcu_pendings(m, &rcu_state);
	248	+ seq_puts(m, "rcu_bh:\n");
	249	+ print_rcu_pendings(m, &rcu_bh_state);
	250	+ return 0;
	251	+}
	252	+
	253	+static int rcu_pending_open(struct inode inode, struct file file)
	254	+{
	255	+ return single_open(file, show_rcu_pending, NULL);
	256	+}
	257	+
	258	+static struct file_operations rcu_pending_fops = {
	259	+ .owner = THIS_MODULE,
	260	+ .open = rcu_pending_open,
	261	+ .read = seq_read,
	262	+ .llseek = seq_lseek,
	263	+ .release = single_release,
	264	+};
	265	+
	266	+static struct dentry *rcudir;
	267	+static struct dentry *datadir;
	268	+static struct dentry *datadir_csv;
	269	+static struct dentry *gpdir;
	270	+static struct dentry *hierdir;
	271	+static struct dentry *rcu_pendingdir;
	272	+
217	273	static int __init rcuclassic_trace_init(void)
218	274	{
219	275	rcudir = debugfs_create_dir("rcu", NULL);
...	...	@@ -238,6 +294,11 @@
238	294	NULL, &rcuhier_fops);
239	295	if (!hierdir)
240	296	goto free_out;
	297	+
	298	+ rcu_pendingdir = debugfs_create_file("rcu_pending", 0444, rcudir,
	299	+ NULL, &rcu_pending_fops);
	300	+ if (!rcu_pendingdir)
	301	+ goto free_out;
241	302	return 0;
242	303	free_out:
243	304	if (datadir)
...	...	@@ -257,6 +318,7 @@
257	318	debugfs_remove(datadir_csv);
258	319	debugfs_remove(gpdir);
259	320	debugfs_remove(hierdir);
	321	+ debugfs_remove(rcu_pendingdir);
260	322	debugfs_remove(rcudir);
261	323	}
262	324