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Subject[patch 3/4] lockstat: measure lock bouncing

__acquire
|
lock _____
| \
| __contended
| |
| wait
| _______/
|/
|
__acquired
|
__release
|
unlock


We measure acquisition and contention bouncing.

This is done by recording a cpu stamp in each lock instance.

Contention bouncing requires the cpu stamp to be set on acquisition. Hence we
move __acquired into the generic path.

__acquired is then used to measure acquisition bouncing by comparing the
current cpu with the old stamp before replacing it.

__contended is used to measure contention bouncing (only useful for preemptable
locks)

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Ingo Molnar <mingo@elte.hu>
---
include/linux/lockdep.h | 17 ++++++++++++++++-
kernel/lockdep.c | 38 ++++++++++++++++++++++++++------------
kernel/lockdep_proc.c | 18 +++++++++++-------
kernel/mutex.c | 2 +-
4 files changed, 54 insertions(+), 21 deletions(-)

Index: linux-2.6/include/linux/lockdep.h
===================================================================
--- linux-2.6.orig/include/linux/lockdep.h
+++ linux-2.6/include/linux/lockdep.h
@@ -130,12 +130,24 @@ struct lock_time {
unsigned long nr;
};

+enum bounce_type {
+ bounce_acquired_write,
+ bounce_acquired_read,
+ bounce_contended_write,
+ bounce_contended_read,
+ nr_bounce_types,
+
+ bounce_acquired = bounce_acquired_write,
+ bounce_contended = bounce_contended_write,
+};
+
struct lock_class_stats {
unsigned long contention_point[4];
struct lock_time read_waittime;
struct lock_time write_waittime;
struct lock_time read_holdtime;
struct lock_time write_holdtime;
+ unsigned long bounces[nr_bounce_types];
};

struct lock_class_stats lock_stats(struct lock_class *class);
@@ -150,6 +162,9 @@ struct lockdep_map {
struct lock_class_key *key;
struct lock_class *class_cache;
const char *name;
+#ifdef CONFIG_LOCK_STAT
+ int cpu;
+#endif
};

/*
@@ -321,8 +336,8 @@ do { \
if (!try(_lock)) { \
lock_contended(&(_lock)->dep_map, _RET_IP_); \
lock(_lock); \
- lock_acquired(&(_lock)->dep_map); \
} \
+ lock_acquired(&(_lock)->dep_map); \
} while (0)

#else /* CONFIG_LOCK_STAT */
Index: linux-2.6/kernel/lockdep.c
===================================================================
--- linux-2.6.orig/kernel/lockdep.c
+++ linux-2.6/kernel/lockdep.c
@@ -177,6 +177,9 @@ struct lock_class_stats lock_stats(struc

lock_time_add(&pcs->read_holdtime, &stats.read_holdtime);
lock_time_add(&pcs->write_holdtime, &stats.write_holdtime);
+
+ for (i = 0; i < ARRAY_SIZE(stats.bounces); i++)
+ stats.bounces[i] += pcs->bounces[i];
}

return stats;
@@ -2328,6 +2331,9 @@ void lockdep_init_map(struct lockdep_map
lock->name = name;
lock->key = key;
lock->class_cache = NULL;
+#ifdef CONFIG_LOCK_STAT
+ lock->cpu = raw_smp_processor_id();
+#endif
if (subclass)
register_lock_class(lock, subclass, 1);
}
@@ -2778,6 +2784,8 @@ found_it:
stats = get_lock_stats(hlock->class);
if (point < ARRAY_SIZE(stats->contention_point))
stats->contention_point[i]++;
+ if (lock->cpu != smp_processor_id())
+ stats->bounces[bounce_contended + !!hlock->read]++;
put_lock_stats(stats);
}

@@ -2789,8 +2797,8 @@ __lock_acquired(struct lockdep_map *lock
struct lock_class_stats *stats;
unsigned int depth;
u64 now;
- s64 waittime;
- int i;
+ s64 waittime = 0;
+ int i, cpu;

depth = curr->lockdep_depth;
if (DEBUG_LOCKS_WARN_ON(!depth))
@@ -2812,19 +2820,25 @@ __lock_acquired(struct lockdep_map *lock
return;

found_it:
- if (!hlock->waittime_stamp)
- return;
-
- now = sched_clock();
- waittime = now - hlock->waittime_stamp;
- hlock->holdtime_stamp = now;
+ cpu = smp_processor_id();
+ if (hlock->waittime_stamp) {
+ now = sched_clock();
+ waittime = now - hlock->waittime_stamp;
+ hlock->holdtime_stamp = now;
+ }

stats = get_lock_stats(hlock->class);
- if (hlock->read)
- lock_time_inc(&stats->read_waittime, waittime);
- else
- lock_time_inc(&stats->write_waittime, waittime);
+ if (waittime) {
+ if (hlock->read)
+ lock_time_inc(&stats->read_waittime, waittime);
+ else
+ lock_time_inc(&stats->write_waittime, waittime);
+ }
+ if (lock->cpu != cpu)
+ stats->bounces[bounce_acquired + !!hlock->read]++;
put_lock_stats(stats);
+
+ lock->cpu = cpu;
}

void lock_contended(struct lockdep_map *lock, unsigned long ip)
Index: linux-2.6/kernel/lockdep_proc.c
===================================================================
--- linux-2.6.orig/kernel/lockdep_proc.c
+++ linux-2.6/kernel/lockdep_proc.c
@@ -430,16 +430,18 @@ static void seq_stats(struct seq_file *m
else
seq_printf(m, "%40s:", name);

+ seq_printf(m, "%14lu ", stats->bounces[bounce_contended_write]);
seq_lock_time(m, &stats->write_waittime);
- seq_puts(m, " ");
+ seq_printf(m, " %14lu ", stats->bounces[bounce_acquired_write]);
seq_lock_time(m, &stats->write_holdtime);
seq_puts(m, "\n");
}

if (stats->read_holdtime.nr) {
seq_printf(m, "%38s-R:", name);
+ seq_printf(m, "%14lu ", stats->bounces[bounce_contended_read]);
seq_lock_time(m, &stats->read_waittime);
- seq_puts(m, " ");
+ seq_printf(m, " %14lu ", stats->bounces[bounce_acquired_read]);
seq_lock_time(m, &stats->read_holdtime);
seq_puts(m, "\n");
}
@@ -469,26 +471,28 @@ static void seq_stats(struct seq_file *m
}
if (i) {
seq_puts(m, "\n");
- seq_line(m, '.', 0, 40 + 1 + 8 * (14 + 1));
+ seq_line(m, '.', 0, 40 + 1 + 10 * (14 + 1));
seq_puts(m, "\n");
}
}

static void seq_header(struct seq_file *m)
{
- seq_printf(m, "lock_stat version 0.1\n");
- seq_line(m, '-', 0, 40 + 1 + 8 * (14 + 1));
- seq_printf(m, "%40s %14s %14s %14s %14s %14s %14s %14s %14s\n",
+ seq_printf(m, "lock_stat version 0.2\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",
"class name",
+ "con-bounces",
"contentions",
"waittime-min",
"waittime-max",
"waittime-total",
+ "acq-bounces",
"acquisitions",
"holdtime-min",
"holdtime-max",
"holdtime-total");
- seq_line(m, '-', 0, 40 + 1 + 8 * (14 + 1));
+ seq_line(m, '-', 0, 40 + 1 + 10 * (14 + 1));
seq_printf(m, "\n");
}

Index: linux-2.6/kernel/mutex.c
===================================================================
--- linux-2.6.orig/kernel/mutex.c
+++ linux-2.6/kernel/mutex.c
@@ -180,8 +180,8 @@ __mutex_lock_common(struct mutex *lock,
spin_lock_mutex(&lock->wait_lock, flags);
}

- lock_acquired(&lock->dep_map);
done:
+ lock_acquired(&lock->dep_map);
/* 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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