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authorPaul E. McKenney <paul.mckenney@linaro.org>2010-09-30 21:26:52 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2010-11-29 22:01:55 -0800
commit9e571a82f0cb205a65a0ea41657f19f22b7fabb8 (patch)
tree64a83a06e18d0fd82af91560a2bf0947e0e3d071
parent24278d148316d2180be6df40e06db013d8b232b8 (diff)
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rcu: add tracing for TINY_RCU and TINY_PREEMPT_RCU
Add tracing for the tiny RCU implementations, including statistics on boosting in the case of TINY_PREEMPT_RCU and RCU_BOOST. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
-rw-r--r--init/Kconfig1
-rw-r--r--kernel/rcutiny.c4
-rw-r--r--kernel/rcutiny_plugin.h232
3 files changed, 226 insertions, 11 deletions
diff --git a/init/Kconfig b/init/Kconfig
index 48efefcac12a..929adf6cb6b4 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -384,7 +384,6 @@ config PREEMPT_RCU
config RCU_TRACE
bool "Enable tracing for RCU"
- depends on TREE_RCU || TREE_PREEMPT_RCU
help
This option provides tracing in RCU which presents stats
in debugfs for debugging RCU implementation.
diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index 93d166582cbb..034493724749 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -144,6 +144,7 @@ static void rcu_process_callbacks(struct rcu_ctrlblk *rcp)
{
struct rcu_head *next, *list;
unsigned long flags;
+ RCU_TRACE(int cb_count = 0);
/* If no RCU callbacks ready to invoke, just return. */
if (&rcp->rcucblist == rcp->donetail)
@@ -169,7 +170,9 @@ static void rcu_process_callbacks(struct rcu_ctrlblk *rcp)
list->func(list);
local_bh_enable();
list = next;
+ RCU_TRACE(cb_count++);
}
+ RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
}
/*
@@ -252,6 +255,7 @@ static void __call_rcu(struct rcu_head *head,
local_irq_save(flags);
*rcp->curtail = head;
rcp->curtail = &head->next;
+ RCU_TRACE(rcp->qlen++);
local_irq_restore(flags);
}
diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index 24f43165f222..f4e0df082d3c 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -23,12 +23,21 @@
*/
#include <linux/kthread.h>
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
+
+#ifdef CONFIG_RCU_TRACE
+#define RCU_TRACE(stmt) stmt
+#else /* #ifdef CONFIG_RCU_TRACE */
+#define RCU_TRACE(stmt)
+#endif /* #else #ifdef CONFIG_RCU_TRACE */
/* Global control variables for rcupdate callback mechanism. */
struct rcu_ctrlblk {
struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */
struct rcu_head **donetail; /* ->next pointer of last "done" CB. */
struct rcu_head **curtail; /* ->next pointer of last CB. */
+ RCU_TRACE(long qlen); /* Number of pending CBs. */
};
/* Definition for rcupdate control block. */
@@ -90,8 +99,26 @@ struct rcu_preempt_ctrlblk {
u8 gpcpu; /* Last grace period blocked by the CPU. */
u8 completed; /* Last grace period completed. */
/* If all three are equal, RCU is idle. */
+#ifdef CONFIG_RCU_BOOST
s8 boosted_this_gp; /* Has boosting already happened? */
unsigned long boost_time; /* When to start boosting (jiffies) */
+#endif /* #ifdef CONFIG_RCU_BOOST */
+#ifdef CONFIG_RCU_TRACE
+ unsigned long n_grace_periods;
+#ifdef CONFIG_RCU_BOOST
+ unsigned long n_tasks_boosted;
+ unsigned long n_exp_boosts;
+ unsigned long n_normal_boosts;
+ unsigned long n_normal_balk_blkd_tasks;
+ unsigned long n_normal_balk_gp_tasks;
+ unsigned long n_normal_balk_boost_tasks;
+ unsigned long n_normal_balk_boosted;
+ unsigned long n_normal_balk_notyet;
+ unsigned long n_normal_balk_nos;
+ unsigned long n_exp_balk_blkd_tasks;
+ unsigned long n_exp_balk_nos;
+#endif /* #ifdef CONFIG_RCU_BOOST */
+#endif /* #ifdef CONFIG_RCU_TRACE */
};
static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = {
@@ -170,6 +197,65 @@ static struct list_head *rcu_next_node_entry(struct task_struct *t)
return np;
}
+#ifdef CONFIG_RCU_TRACE
+
+#ifdef CONFIG_RCU_BOOST
+static void rcu_initiate_boost_trace(void);
+static void rcu_initiate_exp_boost_trace(void);
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
+/*
+ * Dump additional statistice for TINY_PREEMPT_RCU.
+ */
+static void show_tiny_preempt_stats(struct seq_file *m)
+{
+ seq_printf(m, "rcu_preempt: qlen=%ld gp=%lu g%u/p%u/c%u tasks=%c%c%c\n",
+ rcu_preempt_ctrlblk.rcb.qlen,
+ rcu_preempt_ctrlblk.n_grace_periods,
+ rcu_preempt_ctrlblk.gpnum,
+ rcu_preempt_ctrlblk.gpcpu,
+ rcu_preempt_ctrlblk.completed,
+ "T."[list_empty(&rcu_preempt_ctrlblk.blkd_tasks)],
+ "N."[!rcu_preempt_ctrlblk.gp_tasks],
+ "E."[!rcu_preempt_ctrlblk.exp_tasks]);
+#ifdef CONFIG_RCU_BOOST
+ seq_printf(m, " ttb=%c btg=",
+ "B."[!rcu_preempt_ctrlblk.boost_tasks]);
+ switch (rcu_preempt_ctrlblk.boosted_this_gp) {
+ case -1:
+ seq_puts(m, "exp");
+ break;
+ case 0:
+ seq_puts(m, "no");
+ break;
+ case 1:
+ seq_puts(m, "done");
+ break;
+ default:
+ seq_printf(m, "?%d?", rcu_preempt_ctrlblk.boosted_this_gp);
+ }
+ seq_printf(m, " ntb=%lu neb=%lu nnb=%lu j=%04x bt=%04x\n",
+ rcu_preempt_ctrlblk.n_tasks_boosted,
+ rcu_preempt_ctrlblk.n_exp_boosts,
+ rcu_preempt_ctrlblk.n_normal_boosts,
+ (int)(jiffies & 0xffff),
+ (int)(rcu_preempt_ctrlblk.boost_time & 0xffff));
+ seq_printf(m, " %s: nt=%lu gt=%lu bt=%lu b=%lu ny=%lu nos=%lu\n",
+ "normal balk",
+ rcu_preempt_ctrlblk.n_normal_balk_blkd_tasks,
+ rcu_preempt_ctrlblk.n_normal_balk_gp_tasks,
+ rcu_preempt_ctrlblk.n_normal_balk_boost_tasks,
+ rcu_preempt_ctrlblk.n_normal_balk_boosted,
+ rcu_preempt_ctrlblk.n_normal_balk_notyet,
+ rcu_preempt_ctrlblk.n_normal_balk_nos);
+ seq_printf(m, " exp balk: bt=%lu nos=%lu\n",
+ rcu_preempt_ctrlblk.n_exp_balk_blkd_tasks,
+ rcu_preempt_ctrlblk.n_exp_balk_nos);
+#endif /* #ifdef CONFIG_RCU_BOOST */
+}
+
+#endif /* #ifdef CONFIG_RCU_TRACE */
+
#ifdef CONFIG_RCU_BOOST
#include "rtmutex_common.h"
@@ -197,6 +283,7 @@ static int rcu_boost(void)
t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BOOSTED;
raw_local_irq_restore(flags);
rt_mutex_lock(&mtx);
+ RCU_TRACE(rcu_preempt_ctrlblk.n_tasks_boosted++);
rt_mutex_unlock(&mtx);
return rcu_preempt_ctrlblk.boost_tasks != NULL;
}
@@ -206,16 +293,27 @@ static int rcu_boost(void)
* the current grace period, and, if so, tell the rcu_kthread_task to
* start boosting them. If there is an expedited boost in progress,
* we wait for it to complete.
+ *
+ * If there are no blocked readers blocking the current grace period,
+ * return 0 to let the caller know, otherwise return 1. Note that this
+ * return value is independent of whether or not boosting was done.
*/
-static void rcu_initiate_boost(void)
+static int rcu_initiate_boost(void)
{
+ if (!rcu_preempt_blocked_readers_cgp()) {
+ RCU_TRACE(rcu_preempt_ctrlblk.n_normal_balk_blkd_tasks++);
+ return 0;
+ }
if (rcu_preempt_ctrlblk.gp_tasks != NULL &&
rcu_preempt_ctrlblk.boost_tasks == NULL &&
rcu_preempt_ctrlblk.boosted_this_gp == 0 &&
ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time)) {
rcu_preempt_ctrlblk.boost_tasks = rcu_preempt_ctrlblk.gp_tasks;
invoke_rcu_kthread();
- }
+ RCU_TRACE(rcu_preempt_ctrlblk.n_normal_boosts++);
+ } else
+ RCU_TRACE(rcu_initiate_boost_trace());
+ return 1;
}
/*
@@ -231,7 +329,9 @@ static void rcu_initiate_expedited_boost(void)
rcu_preempt_ctrlblk.blkd_tasks.next;
rcu_preempt_ctrlblk.boosted_this_gp = -1;
invoke_rcu_kthread();
- }
+ RCU_TRACE(rcu_preempt_ctrlblk.n_exp_boosts++);
+ } else
+ RCU_TRACE(rcu_initiate_exp_boost_trace());
raw_local_irq_restore(flags);
}
@@ -258,10 +358,13 @@ static int rcu_boost(void)
}
/*
- * If there is no RCU priority boosting, we don't initiate boosting.
+ * If there is no RCU priority boosting, we don't initiate boosting,
+ * but we do indicate whether there are blocked readers blocking the
+ * current grace period.
*/
-static void rcu_initiate_boost(void)
+static int rcu_initiate_boost(void)
{
+ return rcu_preempt_blocked_readers_cgp();
}
/*
@@ -308,13 +411,14 @@ static void rcu_preempt_cpu_qs(void)
current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
/* If there is no GP then there is nothing more to do. */
- if (!rcu_preempt_gp_in_progress() || rcu_preempt_blocked_readers_cgp())
+ if (!rcu_preempt_gp_in_progress())
return;
- /* If there are blocked readers, go check up on boosting. */
- if (rcu_preempt_blocked_readers_cgp()) {
- rcu_initiate_boost();
+ /*
+ * Check up on boosting. If there are no readers blocking the
+ * current grace period, leave.
+ */
+ if (rcu_initiate_boost())
return;
- }
/* Advance callbacks. */
rcu_preempt_ctrlblk.completed = rcu_preempt_ctrlblk.gpnum;
@@ -339,6 +443,7 @@ static void rcu_preempt_start_gp(void)
/* Official start of GP. */
rcu_preempt_ctrlblk.gpnum++;
+ RCU_TRACE(rcu_preempt_ctrlblk.n_grace_periods++);
/* Any blocked RCU readers block new GP. */
if (rcu_preempt_blocked_readers_any())
@@ -591,6 +696,7 @@ void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
local_irq_save(flags);
*rcu_preempt_ctrlblk.nexttail = head;
rcu_preempt_ctrlblk.nexttail = &head->next;
+ RCU_TRACE(rcu_preempt_ctrlblk.rcb.qlen++);
rcu_preempt_start_gp(); /* checks to see if GP needed. */
local_irq_restore(flags);
}
@@ -747,6 +853,18 @@ void exit_rcu(void)
#else /* #ifdef CONFIG_TINY_PREEMPT_RCU */
+#ifdef CONFIG_RCU_TRACE
+
+/*
+ * Because preemptible RCU does not exist, it is not necessary to
+ * dump out its statistics.
+ */
+static void show_tiny_preempt_stats(struct seq_file *m)
+{
+}
+
+#endif /* #ifdef CONFIG_RCU_TRACE */
+
/*
* Because preemptible RCU does not exist, it is never necessary to
* boost preempted RCU readers.
@@ -802,3 +920,97 @@ void __init rcu_scheduler_starting(void)
#else /* #ifdef CONFIG_RCU_BOOST */
#define RCU_BOOST_PRIO 1
#endif /* #else #ifdef CONFIG_RCU_BOOST */
+
+#ifdef CONFIG_RCU_TRACE
+
+#ifdef CONFIG_RCU_BOOST
+
+static void rcu_initiate_boost_trace(void)
+{
+ if (rcu_preempt_ctrlblk.gp_tasks == NULL)
+ rcu_preempt_ctrlblk.n_normal_balk_gp_tasks++;
+ else if (rcu_preempt_ctrlblk.boost_tasks != NULL)
+ rcu_preempt_ctrlblk.n_normal_balk_boost_tasks++;
+ else if (rcu_preempt_ctrlblk.boosted_this_gp != 0)
+ rcu_preempt_ctrlblk.n_normal_balk_boosted++;
+ else if (!ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time))
+ rcu_preempt_ctrlblk.n_normal_balk_notyet++;
+ else
+ rcu_preempt_ctrlblk.n_normal_balk_nos++;
+}
+
+static void rcu_initiate_exp_boost_trace(void)
+{
+ if (list_empty(&rcu_preempt_ctrlblk.blkd_tasks))
+ rcu_preempt_ctrlblk.n_exp_balk_blkd_tasks++;
+ else
+ rcu_preempt_ctrlblk.n_exp_balk_nos++;
+}
+
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
+static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n)
+{
+ unsigned long flags;
+
+ raw_local_irq_save(flags);
+ rcp->qlen -= n;
+ raw_local_irq_restore(flags);
+}
+
+/*
+ * Dump statistics for TINY_RCU, such as they are.
+ */
+static int show_tiny_stats(struct seq_file *m, void *unused)
+{
+ show_tiny_preempt_stats(m);
+ seq_printf(m, "rcu_sched: qlen: %ld\n", rcu_sched_ctrlblk.qlen);
+ seq_printf(m, "rcu_bh: qlen: %ld\n", rcu_bh_ctrlblk.qlen);
+ return 0;
+}
+
+static int show_tiny_stats_open(struct inode *inode, struct file *file)
+{
+ return single_open(file, show_tiny_stats, NULL);
+}
+
+static const struct file_operations show_tiny_stats_fops = {
+ .owner = THIS_MODULE,
+ .open = show_tiny_stats_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = single_release,
+};
+
+static struct dentry *rcudir;
+
+static int __init rcutiny_trace_init(void)
+{
+ struct dentry *retval;
+
+ rcudir = debugfs_create_dir("rcu", NULL);
+ if (!rcudir)
+ goto free_out;
+ retval = debugfs_create_file("rcudata", 0444, rcudir,
+ NULL, &show_tiny_stats_fops);
+ if (!retval)
+ goto free_out;
+ return 0;
+free_out:
+ debugfs_remove_recursive(rcudir);
+ return 1;
+}
+
+static void __exit rcutiny_trace_cleanup(void)
+{
+ debugfs_remove_recursive(rcudir);
+}
+
+module_init(rcutiny_trace_init);
+module_exit(rcutiny_trace_cleanup);
+
+MODULE_AUTHOR("Paul E. McKenney");
+MODULE_DESCRIPTION("Read-Copy Update tracing for tiny implementation");
+MODULE_LICENSE("GPL");
+
+#endif /* #ifdef CONFIG_RCU_TRACE */