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)

[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>

1 files changed, 26 insertions, 12 deletions

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index cb64022851c8..156fce4960c3 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -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)