1 files changed, 115 insertions, 62 deletions

diff --git a/kernel/latencytop.c b/kernel/latencytop.c
index b4e3c85abe7..a02812743a7 100644
--- a/kernel/latencytop.c
+++ b/kernel/latencytop.c
@@ -9,19 +9,56 @@
  * as published by the Free Software Foundation; version 2
  * of the License.
  */
+
+/*
+ * CONFIG_LATENCYTOP enables a kernel latency tracking infrastructure that is
+ * used by the "latencytop" userspace tool. The latency that is tracked is not
+ * the 'traditional' interrupt latency (which is primarily caused by something
+ * else consuming CPU), but instead, it is the latency an application encounters
+ * because the kernel sleeps on its behalf for various reasons.
+ *
+ * This code tracks 2 levels of statistics:
+ * 1) System level latency
+ * 2) Per process latency
+ *
+ * The latency is stored in fixed sized data structures in an accumulated form;
+ * if the "same" latency cause is hit twice, this will be tracked as one entry
+ * in the data structure. Both the count, total accumulated latency and maximum
+ * latency are tracked in this data structure. When the fixed size structure is
+ * full, no new causes are tracked until the buffer is flushed by writing to
+ * the /proc file; the userspace tool does this on a regular basis.
+ *
+ * A latency cause is identified by a stringified backtrace at the point that
+ * the scheduler gets invoked. The userland tool will use this string to
+ * identify the cause of the latency in human readable form.
+ *
+ * The information is exported via /proc/latency_stats and /proc/<pid>/latency.
+ * These files look like this:
+ *
+ * Latency Top version : v0.1
+ * 70 59433 4897 i915_irq_wait drm_ioctl vfs_ioctl do_vfs_ioctl sys_ioctl
+ * |    |    |    |
+ * |    |    |    +----> the stringified backtrace
+ * |    |    +---------> The maximum latency for this entry in microseconds
+ * |    +--------------> The accumulated latency for this entry (microseconds)
+ * +-------------------> The number of times this entry is hit
+ *
+ * (note: the average latency is the accumulated latency divided by the number
+ * of times)
+ */
+
 #include <linux/latencytop.h>
 #include <linux/kallsyms.h>
 #include <linux/seq_file.h>
 #include <linux/notifier.h>
 #include <linux/spinlock.h>
 #include <linux/proc_fs.h>
-#include <linux/module.h>
+#include <linux/export.h>
 #include <linux/sched.h>
 #include <linux/list.h>
-#include <linux/slab.h>
 #include <linux/stacktrace.h>
 
-static DEFINE_SPINLOCK(latency_lock);
+static DEFINE_RAW_SPINLOCK(latency_lock);
 
 #define MAXLR 128
 static struct latency_record latency_record[MAXLR];
@@ -35,23 +72,24 @@ void clear_all_latency_tracing(struct task_struct *p)
 	if (!latencytop_enabled)
 		return;
 
-	spin_lock_irqsave(&latency_lock, flags);
+	raw_spin_lock_irqsave(&latency_lock, flags);
 	memset(&p->latency_record, 0, sizeof(p->latency_record));
 	p->latency_record_count = 0;
-	spin_unlock_irqrestore(&latency_lock, flags);
+	raw_spin_unlock_irqrestore(&latency_lock, flags);
 }
 
 static void clear_global_latency_tracing(void)
 {
 	unsigned long flags;
 
-	spin_lock_irqsave(&latency_lock, flags);
+	raw_spin_lock_irqsave(&latency_lock, flags);
 	memset(&latency_record, 0, sizeof(latency_record));
-	spin_unlock_irqrestore(&latency_lock, flags);
+	raw_spin_unlock_irqrestore(&latency_lock, flags);
 }
 
 static void __sched
-account_global_scheduler_latency(struct task_struct *tsk, struct latency_record *lat)
+account_global_scheduler_latency(struct task_struct *tsk,
+				 struct latency_record *lat)
 {
 	int firstnonnull = MAXLR + 1;
 	int i;
@@ -64,21 +102,24 @@ account_global_scheduler_latency(struct task_struct *tsk, struct latency_record
 		return;
 
 	for (i = 0; i < MAXLR; i++) {
-		int q;
-		int same = 1;
+		int q, same = 1;
+
 		/* Nothing stored: */
 		if (!latency_record[i].backtrace[0]) {
 			if (firstnonnull > i)
 				firstnonnull = i;
 			continue;
 		}
-		for (q = 0 ; q < LT_BACKTRACEDEPTH ; q++) {
-			if (latency_record[i].backtrace[q] !=
-				lat->backtrace[q])
+		for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
+			unsigned long record = lat->backtrace[q];
+
+			if (latency_record[i].backtrace[q] != record) {
 				same = 0;
-			if (same && lat->backtrace[q] == 0)
 				break;
-			if (same && lat->backtrace[q] == ULONG_MAX)
+			}
+
+			/* 0 and ULONG_MAX entries mean end of backtrace: */
+			if (record == 0 || record == ULONG_MAX)
 				break;
 		}
 		if (same) {
@@ -98,59 +139,77 @@ account_global_scheduler_latency(struct task_struct *tsk, struct latency_record
 	memcpy(&latency_record[i], lat, sizeof(struct latency_record));
 }
 
-static inline void store_stacktrace(struct task_struct *tsk, struct latency_record *lat)
+/*
+ * Iterator to store a backtrace into a latency record entry
+ */
+static inline void store_stacktrace(struct task_struct *tsk,
+					struct latency_record *lat)
 {
 	struct stack_trace trace;
 
 	memset(&trace, 0, sizeof(trace));
 	trace.max_entries = LT_BACKTRACEDEPTH;
 	trace.entries = &lat->backtrace[0];
-	trace.skip = 0;
 	save_stack_trace_tsk(tsk, &trace);
 }
 
+/**
+ * __account_scheduler_latency - record an occurred latency
+ * @tsk - the task struct of the task hitting the latency
+ * @usecs - the duration of the latency in microseconds
+ * @inter - 1 if the sleep was interruptible, 0 if uninterruptible
+ *
+ * This function is the main entry point for recording latency entries
+ * as called by the scheduler.
+ *
+ * This function has a few special cases to deal with normal 'non-latency'
+ * sleeps: specifically, interruptible sleep longer than 5 msec is skipped
+ * since this usually is caused by waiting for events via select() and co.
+ *
+ * Negative latencies (caused by time going backwards) are also explicitly
+ * skipped.
+ */
 void __sched
-account_scheduler_latency(struct task_struct *tsk, int usecs, int inter)
+__account_scheduler_latency(struct task_struct *tsk, int usecs, int inter)
 {
 	unsigned long flags;
 	int i, q;
 	struct latency_record lat;
 
-	if (!latencytop_enabled)
-		return;
-
 	/* Long interruptible waits are generally user requested... */
 	if (inter && usecs > 5000)
 		return;
 
+	/* Negative sleeps are time going backwards */
+	/* Zero-time sleeps are non-interesting */
+	if (usecs <= 0)
+		return;
+
 	memset(&lat, 0, sizeof(lat));
 	lat.count = 1;
 	lat.time = usecs;
 	lat.max = usecs;
 	store_stacktrace(tsk, &lat);
 
-	spin_lock_irqsave(&latency_lock, flags);
+	raw_spin_lock_irqsave(&latency_lock, flags);
 
 	account_global_scheduler_latency(tsk, &lat);
 
-	/*
-	 * short term hack; if we're > 32 we stop; future we recycle:
-	 */
-	tsk->latency_record_count++;
-	if (tsk->latency_record_count >= LT_SAVECOUNT)
-		goto out_unlock;
-
-	for (i = 0; i < LT_SAVECOUNT ; i++) {
+	for (i = 0; i < tsk->latency_record_count; i++) {
 		struct latency_record *mylat;
 		int same = 1;
+
 		mylat = &tsk->latency_record[i];
-		for (q = 0 ; q < LT_BACKTRACEDEPTH ; q++) {
-			if (mylat->backtrace[q] !=
-				lat.backtrace[q])
+		for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
+			unsigned long record = lat.backtrace[q];
+
+			if (mylat->backtrace[q] != record) {
 				same = 0;
-			if (same && lat.backtrace[q] == 0)
 				break;
-			if (same && lat.backtrace[q] == ULONG_MAX)
+			}
+
+			/* 0 and ULONG_MAX entries mean end of backtrace: */
+			if (record == 0 || record == ULONG_MAX)
 				break;
 		}
 		if (same) {
@@ -162,12 +221,18 @@ account_scheduler_latency(struct task_struct *tsk, int usecs, int inter)
 		}
 	}
 
+	/*
+	 * short term hack; if we're > 32 we stop; future we recycle:
+	 */
+	if (tsk->latency_record_count >= LT_SAVECOUNT)
+		goto out_unlock;
+
 	/* Allocated a new one: */
-	i = tsk->latency_record_count;
+	i = tsk->latency_record_count++;
 	memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record));
 
 out_unlock:
-	spin_unlock_irqrestore(&latency_lock, flags);
+	raw_spin_unlock_irqrestore(&latency_lock, flags);
 }
 
 static int lstats_show(struct seq_file *m, void *v)
@@ -177,26 +242,21 @@ static int lstats_show(struct seq_file *m, void *v)
 	seq_puts(m, "Latency Top version : v0.1\n");
 
 	for (i = 0; i < MAXLR; i++) {
-		if (latency_record[i].backtrace[0]) {
+		struct latency_record *lr = &latency_record[i];
+
+		if (lr->backtrace[0]) {
 			int q;
-			seq_printf(m, "%i %li %li ",
-				latency_record[i].count,
-				latency_record[i].time,
-				latency_record[i].max);
+			seq_printf(m, "%i %lu %lu",
+				   lr->count, lr->time, lr->max);
 			for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
-				char sym[KSYM_NAME_LEN];
-				char *c;
-				if (!latency_record[i].backtrace[q])
+				unsigned long bt = lr->backtrace[q];
+				if (!bt)
 					break;
-				if (latency_record[i].backtrace[q] == ULONG_MAX)
+				if (bt == ULONG_MAX)
 					break;
-				sprint_symbol(sym, latency_record[i].backtrace[q]);
-				c = strchr(sym, '+');
-				if (c)
-					*c = 0;
-				seq_printf(m, "%s ", sym);
+				seq_printf(m, " %ps", (void *)bt);
 			}
-			seq_printf(m, "\n");
+			seq_puts(m, "\n");
 		}
 	}
 	return 0;
@@ -216,7 +276,7 @@ static int lstats_open(struct inode *inode, struct file *filp)
 	return single_open(filp, lstats_show, NULL);
 }
 
-static struct file_operations lstats_fops = {
+static const struct file_operations lstats_fops = {
 	.open		= lstats_open,
 	.read		= seq_read,
 	.write		= lstats_write,
@@ -226,14 +286,7 @@ static struct file_operations lstats_fops = {
 
 static int __init init_lstats_procfs(void)
 {
-	struct proc_dir_entry *pe;
-
-	pe = create_proc_entry("latency_stats", 0644, NULL);
-	if (!pe)
-		return -ENOMEM;
-
-	pe->proc_fops = &lstats_fops;
-
+	proc_create("latency_stats", 0644, NULL, &lstats_fops);
 	return 0;
 }
-__initcall(init_lstats_procfs);
+device_initcall(init_lstats_procfs);