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Subject[PATCH] lockstat: contend with points
From
Date
Subject: lockstat: contend with points
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Thu Oct 16 23:17:09 CEST 2008

We currently only provide points that have to wait on contention, also
lists the points we have to wait for.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
Documentation/lockstat.txt | 50 ++++++++++++++++++++++++++++-----------------
include/linux/lockdep.h | 13 ++++++++---
kernel/lockdep.c | 33 ++++++++++++++++++-----------
kernel/lockdep_proc.c | 21 +++++++++++++++++-
kernel/mutex.c | 2 -
5 files changed, 82 insertions(+), 37 deletions(-)

Index: linux-2.6/Documentation/lockstat.txt
===================================================================
--- linux-2.6.orig/Documentation/lockstat.txt
+++ linux-2.6/Documentation/lockstat.txt
@@ -71,34 +71,48 @@ Look at the current lock statistics:

# less /proc/lock_stat

-01 lock_stat version 0.2
+01 lock_stat version 0.3
02 -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
03 class name con-bounces contentions waittime-min waittime-max waittime-total acq-bounces acquisitions holdtime-min holdtime-max holdtime-total
04 -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
05
-06 &inode->i_data.tree_lock-W: 15 21657 0.18 1093295.30 11547131054.85 58 10415 0.16 87.51 6387.60
-07 &inode->i_data.tree_lock-R: 0 0 0.00 0.00 0.00 23302 231198 0.25 8.45 98023.38
-08 --------------------------
-09 &inode->i_data.tree_lock 0 [<ffffffff8027c08f>] add_to_page_cache+0x5f/0x190
-10
-11 ...............................................................................................................................................................................................
-12
-13 dcache_lock: 1037 1161 0.38 45.32 774.51 6611 243371 0.15 306.48 77387.24
-14 -----------
-15 dcache_lock 180 [<ffffffff802c0d7e>] sys_getcwd+0x11e/0x230
-16 dcache_lock 165 [<ffffffff802c002a>] d_alloc+0x15a/0x210
-17 dcache_lock 33 [<ffffffff8035818d>] _atomic_dec_and_lock+0x4d/0x70
-18 dcache_lock 1 [<ffffffff802beef8>] shrink_dcache_parent+0x18/0x130
+06 &mm->mmap_sem-W: 233 538 18446744073708 22924.27 607243.51 1342 45806 1.71 8595.89 1180582.34
+07 &mm->mmap_sem-R: 205 587 18446744073708 28403.36 731975.00 1940 412426 0.58 187825.45 6307502.88
+08 ---------------
+09 &mm->mmap_sem 487 [<ffffffff8053491f>] do_page_fault+0x466/0x928
+10 &mm->mmap_sem 179 [<ffffffff802a6200>] sys_mprotect+0xcd/0x21d
+11 &mm->mmap_sem 279 [<ffffffff80210a57>] sys_mmap+0x75/0xce
+12 &mm->mmap_sem 76 [<ffffffff802a490b>] sys_munmap+0x32/0x59
+13 ---------------
+14 &mm->mmap_sem 270 [<ffffffff80210a57>] sys_mmap+0x75/0xce
+15 &mm->mmap_sem 431 [<ffffffff8053491f>] do_page_fault+0x466/0x928
+16 &mm->mmap_sem 138 [<ffffffff802a490b>] sys_munmap+0x32/0x59
+17 &mm->mmap_sem 145 [<ffffffff802a6200>] sys_mprotect+0xcd/0x21d
+18
+19 ...............................................................................................................................................................................................
+20
+21 dcache_lock: 621 623 0.52 118.26 1053.02 6745 91930 0.29 316.29 118423.41
+22 -----------
+23 dcache_lock 179 [<ffffffff80378274>] _atomic_dec_and_lock+0x34/0x54
+24 dcache_lock 113 [<ffffffff802cc17b>] d_alloc+0x19a/0x1eb
+25 dcache_lock 99 [<ffffffff802ca0dc>] d_rehash+0x1b/0x44
+26 dcache_lock 104 [<ffffffff802cbca0>] d_instantiate+0x36/0x8a
+27 -----------
+28 dcache_lock 192 [<ffffffff80378274>] _atomic_dec_and_lock+0x34/0x54
+29 dcache_lock 98 [<ffffffff802ca0dc>] d_rehash+0x1b/0x44
+30 dcache_lock 72 [<ffffffff802cc17b>] d_alloc+0x19a/0x1eb
+31 dcache_lock 112 [<ffffffff802cbca0>] d_instantiate+0x36/0x8a

This excerpt shows the first two lock class statistics. Line 01 shows the
output version - each time the format changes this will be updated. Line 02-04
-show the header with column descriptions. Lines 05-10 and 13-18 show the actual
+show the header with column descriptions. Lines 05-18 and 20-31 show the actual
statistics. These statistics come in two parts; the actual stats separated by a
-short separator (line 08, 14) from the contention points.
+short separator (line 08, 13) from the contention points.

-The first lock (05-10) is a read/write lock, and shows two lines above the
+The first lock (05-18) is a read/write lock, and shows two lines above the
short separator. The contention points don't match the column descriptors,
-they have two: contentions and [<IP>] symbol.
+they have two: contentions and [<IP>] symbol. The second set of contention
+points are the points we're contending with.


View the top contending locks:
Index: linux-2.6/include/linux/lockdep.h
===================================================================
--- linux-2.6.orig/include/linux/lockdep.h
+++ linux-2.6/include/linux/lockdep.h
@@ -73,6 +73,8 @@ struct lock_class_key {
struct lockdep_subclass_key subkeys[MAX_LOCKDEP_SUBCLASSES];
};

+#define LOCKSTAT_POINTS 4
+
/*
* The lock-class itself:
*/
@@ -119,7 +121,8 @@ struct lock_class {
int name_version;

#ifdef CONFIG_LOCK_STAT
- unsigned long contention_point[4];
+ unsigned long contention_point[LOCKSTAT_POINTS];
+ unsigned long contending_point[LOCKSTAT_POINTS];
#endif
};

@@ -144,6 +147,7 @@ enum bounce_type {

struct lock_class_stats {
unsigned long contention_point[4];
+ unsigned long contending_point[4];
struct lock_time read_waittime;
struct lock_time write_waittime;
struct lock_time read_holdtime;
@@ -165,6 +169,7 @@ struct lockdep_map {
const char *name;
#ifdef CONFIG_LOCK_STAT
int cpu;
+ unsigned long ip;
#endif
};

@@ -355,7 +360,7 @@ struct lock_class_key { };
#ifdef CONFIG_LOCK_STAT

extern void lock_contended(struct lockdep_map *lock, unsigned long ip);
-extern void lock_acquired(struct lockdep_map *lock);
+extern void lock_acquired(struct lockdep_map *lock, unsigned long ip);

#define LOCK_CONTENDED(_lock, try, lock) \
do { \
@@ -363,13 +368,13 @@ do { \
lock_contended(&(_lock)->dep_map, _RET_IP_); \
lock(_lock); \
} \
- lock_acquired(&(_lock)->dep_map); \
+ lock_acquired(&(_lock)->dep_map, _RET_IP_); \
} while (0)

#else /* CONFIG_LOCK_STAT */

#define lock_contended(lockdep_map, ip) do {} while (0)
-#define lock_acquired(lockdep_map) do {} while (0)
+#define lock_acquired(lockdep_map, ip) do {} while (0)

#define LOCK_CONTENDED(_lock, try, lock) \
lock(_lock)
Index: linux-2.6/kernel/lockdep.c
===================================================================
--- linux-2.6.orig/kernel/lockdep.c
+++ linux-2.6/kernel/lockdep.c
@@ -136,16 +136,16 @@ static inline struct lock_class *hlock_c
#ifdef CONFIG_LOCK_STAT
static DEFINE_PER_CPU(struct lock_class_stats[MAX_LOCKDEP_KEYS], lock_stats);

-static int lock_contention_point(struct lock_class *class, unsigned long ip)
+static int lock_point(unsigned long points[], unsigned long ip)
{
int i;

- for (i = 0; i < ARRAY_SIZE(class->contention_point); i++) {
- if (class->contention_point[i] == 0) {
- class->contention_point[i] = ip;
+ for (i = 0; i < LOCKSTAT_POINTS; i++) {
+ if (points[i] == 0) {
+ points[i] = ip;
break;
}
- if (class->contention_point[i] == ip)
+ if (points[i] == ip)
break;
}

@@ -185,6 +185,9 @@ struct lock_class_stats lock_stats(struc
for (i = 0; i < ARRAY_SIZE(stats.contention_point); i++)
stats.contention_point[i] += pcs->contention_point[i];

+ for (i = 0; i < ARRAY_SIZE(stats.contending_point); i++)
+ stats.contending_point[i] += pcs->contending_point[i];
+
lock_time_add(&pcs->read_waittime, &stats.read_waittime);
lock_time_add(&pcs->write_waittime, &stats.write_waittime);

@@ -209,6 +212,7 @@ void clear_lock_stats(struct lock_class
memset(cpu_stats, 0, sizeof(struct lock_class_stats));
}
memset(class->contention_point, 0, sizeof(class->contention_point));
+ memset(class->contending_point, 0, sizeof(class->contending_point));
}

static struct lock_class_stats *get_lock_stats(struct lock_class *class)
@@ -3001,7 +3005,7 @@ __lock_contended(struct lockdep_map *loc
struct held_lock *hlock, *prev_hlock;
struct lock_class_stats *stats;
unsigned int depth;
- int i, point;
+ int i, contention_point, contending_point;

depth = curr->lockdep_depth;
if (DEBUG_LOCKS_WARN_ON(!depth))
@@ -3025,18 +3029,22 @@ __lock_contended(struct lockdep_map *loc
found_it:
hlock->waittime_stamp = sched_clock();

- point = lock_contention_point(hlock_class(hlock), ip);
+ contention_point = lock_point(hlock_class(hlock)->contention_point, ip);
+ contending_point = lock_point(hlock_class(hlock)->contending_point,
+ lock->ip);

stats = get_lock_stats(hlock_class(hlock));
- if (point < ARRAY_SIZE(stats->contention_point))
- stats->contention_point[point]++;
+ if (contention_point < LOCKSTAT_POINTS)
+ stats->contention_point[contention_point]++;
+ if (contending_point < LOCKSTAT_POINTS)
+ stats->contending_point[contending_point]++;
if (lock->cpu != smp_processor_id())
stats->bounces[bounce_contended + !!hlock->read]++;
put_lock_stats(stats);
}

static void
-__lock_acquired(struct lockdep_map *lock)
+__lock_acquired(struct lockdep_map *lock, unsigned long ip)
{
struct task_struct *curr = current;
struct held_lock *hlock, *prev_hlock;
@@ -3085,6 +3093,7 @@ found_it:
put_lock_stats(stats);

lock->cpu = cpu;
+ lock->ip = ip;
}

void lock_contended(struct lockdep_map *lock, unsigned long ip)
@@ -3106,7 +3115,7 @@ void lock_contended(struct lockdep_map *
}
EXPORT_SYMBOL_GPL(lock_contended);

-void lock_acquired(struct lockdep_map *lock)
+void lock_acquired(struct lockdep_map *lock, unsigned long ip)
{
unsigned long flags;

@@ -3119,7 +3128,7 @@ void lock_acquired(struct lockdep_map *l
raw_local_irq_save(flags);
check_flags(flags);
current->lockdep_recursion = 1;
- __lock_acquired(lock);
+ __lock_acquired(lock, ip);
current->lockdep_recursion = 0;
raw_local_irq_restore(flags);
}
Index: linux-2.6/kernel/lockdep_proc.c
===================================================================
--- linux-2.6.orig/kernel/lockdep_proc.c
+++ linux-2.6/kernel/lockdep_proc.c
@@ -556,7 +556,7 @@ static void seq_stats(struct seq_file *m
if (stats->read_holdtime.nr)
namelen += 2;

- for (i = 0; i < ARRAY_SIZE(class->contention_point); i++) {
+ for (i = 0; i < LOCKSTAT_POINTS; i++) {
char sym[KSYM_SYMBOL_LEN];
char ip[32];

@@ -573,6 +573,23 @@ static void seq_stats(struct seq_file *m
stats->contention_point[i],
ip, sym);
}
+ for (i = 0; i < LOCKSTAT_POINTS; i++) {
+ char sym[KSYM_SYMBOL_LEN];
+ char ip[32];
+
+ if (class->contending_point[i] == 0)
+ break;
+
+ if (!i)
+ seq_line(m, '-', 40-namelen, namelen);
+
+ sprint_symbol(sym, class->contending_point[i]);
+ snprintf(ip, sizeof(ip), "[<%p>]",
+ (void *)class->contending_point[i]);
+ seq_printf(m, "%40s %14lu %29s %s\n", name,
+ stats->contending_point[i],
+ ip, sym);
+ }
if (i) {
seq_puts(m, "\n");
seq_line(m, '.', 0, 40 + 1 + 10 * (14 + 1));
@@ -582,7 +599,7 @@ static void seq_stats(struct seq_file *m

static void seq_header(struct seq_file *m)
{
- seq_printf(m, "lock_stat version 0.2\n");
+ seq_printf(m, "lock_stat version 0.3\n");
seq_line(m, '-', 0, 40 + 1 + 10 * (14 + 1));
seq_printf(m, "%40s %14s %14s %14s %14s %14s %14s %14s %14s "
"%14s %14s\n",
Index: linux-2.6/kernel/mutex.c
===================================================================
--- linux-2.6.orig/kernel/mutex.c
+++ linux-2.6/kernel/mutex.c
@@ -184,7 +184,7 @@ __mutex_lock_common(struct mutex *lock,
}

done:
- lock_acquired(&lock->dep_map);
+ lock_acquired(&lock->dep_map, ip);
/* got the lock - rejoice! */
mutex_remove_waiter(lock, &waiter, task_thread_info(task));
debug_mutex_set_owner(lock, task_thread_info(task));



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