lockstat: measure lock bouncing
Peter Zijlstra [Thu, 19 Jul 2007 08:49:00 +0000 (01:49 -0700)]
    __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)

[akpm@linux-foundation.org: cleanups]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/lockdep.h
kernel/lockdep.c
kernel/lockdep_proc.c
kernel/mutex.c

index 3d3386b..0e843bf 100644 (file)
@@ -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 cb64022..156fce4 100644 (file)
@@ -177,6 +177,9 @@ struct lock_class_stats lock_stats(struct lock_class *class)
 
                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;
@@ -2325,6 +2328,9 @@ void lockdep_init_map(struct lockdep_map *lock, const char *name,
        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);
 }
@@ -2775,6 +2781,8 @@ 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);
 }
 
@@ -2786,8 +2794,8 @@ __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))
@@ -2809,19 +2817,25 @@ __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 39163ed..7ff8013 100644 (file)
@@ -430,16 +430,18 @@ static void seq_stats(struct seq_file *m, struct lock_stat_data *data)
                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 +471,29 @@ static void seq_stats(struct seq_file *m, struct lock_stat_data *data)
        }
        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 7a3f327..691b865 100644 (file)
@@ -180,8 +180,8 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass)
                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));