Date:	Thu, 9 Oct 2008 20:44:21 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, rjw@...k.pl, dipankar@...ibm.com,
	tglx@...uxtronix.de, andi@...stfloor.org
Subject: [PATCH] v2 rudimentary tracing for Classic RCU

Hello!

This is a tracing patch for Classic RCU, which creates an "rcu/rcucb"
file in debugfs.  This patch can be handy when you need to work out
why RCU is refusing to end the current grace period.

Changes since v1:  Adds (crude) tracing for rcu_data structures.

Additional work needed:  Don't print rcu_data for offline CPUs.
			 Documentation update.

Reading from the file results in something like the following:

	rcu: cur=1129  completed=1128  np=0  s=0
		0,3,7
	rcu_bh: cur=-287  completed=-287  np=0  s=0

	online: 0-7

The first two lines are for rcu, the second two for rcu_bh.
The cur= is the current grace-period number, and the completed=
is the number of the last completed grace period.  If these two
numbers are equal, the corresponding flavor of RCU is idle.
The np= is a flag indicating that an additional RCU grace period
beyond the current one will be required.  The s=, if non-zero,
indicates that a round of reschedule IPIs has been send to
attempt to expedite the current grace period.

The second and fourth lines are a comma/dash-separated list of
the CPUs that have not yet reported a quiescent state for the
current grace period (CPUs 0, 3, and 7 for "rcu" above).

The last line lists the online CPUs.

Tested on x86 and Power.

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

 include/linux/rcuclassic.h |    3 
 kernel/Kconfig.preempt     |    1 
 kernel/Makefile            |    2 
 kernel/rcuclassic.c        |    4 -
 kernel/rcuclassic_trace.c  |  179 +++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 186 insertions(+), 3 deletions(-)

diff --git a/include/linux/rcuclassic.h b/include/linux/rcuclassic.h
index 4ab8436..061a272 100644
--- a/include/linux/rcuclassic.h
+++ b/include/linux/rcuclassic.h
@@ -54,6 +54,9 @@ struct rcu_ctrlblk {
 				 /* for current batch to proceed.        */
 } ____cacheline_internodealigned_in_smp;
 
+extern struct rcu_ctrlblk rcu_ctrlblk;
+extern struct rcu_ctrlblk rcu_bh_ctrlblk;
+
 /* Is batch a before batch b ? */
 static inline int rcu_batch_before(long a, long b)
 {
diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
index 9fdba03..ba32338 100644
--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -68,7 +68,6 @@ config PREEMPT_RCU
 
 config RCU_TRACE
 	bool "Enable tracing for RCU - currently stats in debugfs"
-	depends on PREEMPT_RCU
 	select DEBUG_FS
 	default y
 	help
diff --git a/kernel/Makefile b/kernel/Makefile
index 4e1d7df..e0bfce7 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -77,6 +77,8 @@ obj-$(CONFIG_CLASSIC_RCU) += rcuclassic.o
 obj-$(CONFIG_PREEMPT_RCU) += rcupreempt.o
 ifeq ($(CONFIG_PREEMPT_RCU),y)
 obj-$(CONFIG_RCU_TRACE) += rcupreempt_trace.o
+else
+obj-$(CONFIG_RCU_TRACE) += rcuclassic_trace.o
 endif
 obj-$(CONFIG_RELAY) += relay.o
 obj-$(CONFIG_SYSCTL) += utsname_sysctl.o
diff --git a/kernel/rcuclassic.c b/kernel/rcuclassic.c
index aad93cd..517eaa9 100644
--- a/kernel/rcuclassic.c
+++ b/kernel/rcuclassic.c
@@ -57,13 +57,13 @@ EXPORT_SYMBOL_GPL(rcu_lock_map);
 
 
 /* Definition for rcupdate control block. */
-static struct rcu_ctrlblk rcu_ctrlblk = {
+struct rcu_ctrlblk rcu_ctrlblk = {
 	.cur = -300,
 	.completed = -300,
 	.lock = __SPIN_LOCK_UNLOCKED(&rcu_ctrlblk.lock),
 	.cpumask = CPU_MASK_NONE,
 };
-static struct rcu_ctrlblk rcu_bh_ctrlblk = {
+struct rcu_ctrlblk rcu_bh_ctrlblk = {
 	.cur = -300,
 	.completed = -300,
 	.lock = __SPIN_LOCK_UNLOCKED(&rcu_bh_ctrlblk.lock),
diff --git a/kernel/rcuclassic_trace.c b/kernel/rcuclassic_trace.c
new file mode 100644
index 0000000..a478256
--- /dev/null
+++ b/kernel/rcuclassic_trace.c
@@ -0,0 +1,179 @@
+/*
+ * Read-Copy Update tracing for classic implementation
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright IBM Corporation, 2008
+ *
+ * Papers:  http://www.rdrop.com/users/paulmck/RCU
+ *
+ * For detailed explanation of Read-Copy Update mechanism see -
+ * 		Documentation/RCU
+ *
+ */
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/spinlock.h>
+#include <linux/smp.h>
+#include <linux/rcupdate.h>
+#include <linux/interrupt.h>
+#include <linux/sched.h>
+#include <asm/atomic.h>
+#include <linux/bitops.h>
+#include <linux/module.h>
+#include <linux/completion.h>
+#include <linux/moduleparam.h>
+#include <linux/percpu.h>
+#include <linux/notifier.h>
+#include <linux/cpu.h>
+#include <linux/mutex.h>
+#include <linux/debugfs.h>
+
+static DEFINE_MUTEX(rcuclassic_trace_mutex);
+static char *rcuclassic_trace_buf;
+#define RCUCLASSIC_TRACE_BUF_SIZE (128 * num_possible_cpus() + 100)
+
+static int print_one_rcu_data(struct rcu_data *rdp, char *buf, char *ebuf)
+{
+	int cnt = 0;
+
+	if (cpu_is_offline(rdp->cpu))
+		return 0;
+	cnt += snprintf(&buf[cnt], ebuf - &buf[cnt],
+		"%3d%cqb=%ld b=%ld pq=%d qsp=%d ql=%ld bl=%ld\n",
+		rdp->cpu, cpu_is_offline(rdp->cpu) ? '!' : ' ',
+		rdp->quiescbatch, rdp->batch, rdp->passed_quiesc,
+		rdp->qs_pending, rdp->qlen, rdp->blimit);
+	return cnt;
+}
+
+#define PRINT_RCU_DATA(name, buf, ebuf) \
+	do { \
+		int _p_r_d_i; \
+		\
+		for_each_possible_cpu(_p_r_d_i) \
+			(buf) += print_one_rcu_data(&per_cpu(name, _p_r_d_i), \
+						    buf, ebuf); \
+	} while (0)
+
+static ssize_t rcudata_read(struct file *filp, char __user *buffer,
+				size_t count, loff_t *ppos)
+{
+	ssize_t bcount;
+	char *buf = rcuclassic_trace_buf;
+	char *ebuf = &rcuclassic_trace_buf[RCUCLASSIC_TRACE_BUF_SIZE];
+
+	mutex_lock(&rcuclassic_trace_mutex);
+	buf += snprintf(buf, ebuf - buf, "rcu:\n");
+	PRINT_RCU_DATA(rcu_data, buf, ebuf);
+	buf += snprintf(buf, ebuf - buf, "rcu_bh:\n");
+	PRINT_RCU_DATA(rcu_bh_data, buf, ebuf);
+	bcount = simple_read_from_buffer(buffer, count, ppos,
+			rcuclassic_trace_buf, strlen(rcuclassic_trace_buf));
+	mutex_unlock(&rcuclassic_trace_mutex);
+	return bcount;
+}
+
+static int print_one_rcu_ctrlblk(struct rcu_ctrlblk *rcp, char *buf, char *ebuf)
+{
+	int cnt = 0;
+
+	cnt += snprintf(&buf[cnt], ebuf - &buf[cnt], "cur=%ld  completed=%ld  "
+			"np=%d  s=%d\n\t",
+			rcp->cur, rcp->completed,
+			rcp->next_pending, rcp->signaled);
+	cnt += cpulist_scnprintf(&buf[cnt], ebuf - &buf[cnt], rcp->cpumask);
+	cnt += snprintf(&buf[cnt], ebuf - &buf[cnt], "\n");
+	return cnt;
+}
+
+static ssize_t rcucb_read(struct file *filp, char __user *buffer,
+				size_t count, loff_t *ppos)
+{
+	ssize_t bcount;
+	char *buf = rcuclassic_trace_buf;
+	char *ebuf = &rcuclassic_trace_buf[RCUCLASSIC_TRACE_BUF_SIZE];
+
+	mutex_lock(&rcuclassic_trace_mutex);
+	buf += snprintf(buf, ebuf - buf, "rcu: ");
+	buf += print_one_rcu_ctrlblk(&rcu_ctrlblk, buf, ebuf);
+	buf += snprintf(buf, ebuf - buf, "rcu_bh: ");
+	buf += print_one_rcu_ctrlblk(&rcu_bh_ctrlblk, buf, ebuf);
+	buf += snprintf(buf, ebuf - buf, "online: ");
+	buf += cpulist_scnprintf(buf, ebuf - buf, cpu_online_map);
+	buf += snprintf(buf, ebuf - buf, "\n");
+	bcount = simple_read_from_buffer(buffer, count, ppos,
+			rcuclassic_trace_buf, strlen(rcuclassic_trace_buf));
+	mutex_unlock(&rcuclassic_trace_mutex);
+	return bcount;
+}
+
+static struct file_operations rcudata_fops = {
+	.owner = THIS_MODULE,
+	.read = rcudata_read,
+};
+
+static struct file_operations rcucb_fops = {
+	.owner = THIS_MODULE,
+	.read = rcucb_read,
+};
+
+static struct dentry *rcudir, *datadir, *cbdir;
+static int rcuclassic_debugfs_init(void)
+{
+	rcudir = debugfs_create_dir("rcu", NULL);
+	if (!rcudir)
+		goto out;
+	datadir = debugfs_create_file("rcudata", 0444, rcudir,
+				      NULL, &rcudata_fops);
+	if (!datadir)
+		goto free_out;
+	cbdir = debugfs_create_file("rcucb", 0444, rcudir, NULL, &rcucb_fops);
+	if (!cbdir)
+		goto free_out;
+	return 0;
+free_out:
+	if (datadir)
+		debugfs_remove(datadir);
+	debugfs_remove(rcudir);
+out:
+	return 1;
+}
+
+static int __init rcuclassic_trace_init(void)
+{
+	int ret;
+
+	rcuclassic_trace_buf = kmalloc(RCUCLASSIC_TRACE_BUF_SIZE, GFP_KERNEL);
+	if (!rcuclassic_trace_buf)
+		return 1;
+	ret = rcuclassic_debugfs_init();
+	if (ret)
+		kfree(rcuclassic_trace_buf);
+	return ret;
+}
+
+static void __exit rcuclassic_trace_cleanup(void)
+{
+	debugfs_remove(datadir);
+	debugfs_remove(cbdir);
+	debugfs_remove(rcudir);
+	kfree(rcuclassic_trace_buf);
+}
+
+
+module_init(rcuclassic_trace_init);
+module_exit(rcuclassic_trace_cleanup);
--
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