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tracing/lockdep: report the time waited for a lock

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While trying to optimize the new lock on reiserfs to replace
the bkl, I find the lock tracing very useful though it lacks
something important for performance (and latency) instrumentation:
the time a task waits for a lock.

That's what this patch implements:

  bash-4816  [000]   202.652815: lock_contended: lock_contended: &sb->s_type->i_mutex_key
  bash-4816  [000]   202.652819: lock_acquired: &rq->lock (0.000 us)
 <...>-4787  [000]   202.652825: lock_acquired: &rq->lock (0.000 us)
 <...>-4787  [000]   202.652829: lock_acquired: &rq->lock (0.000 us)
  bash-4816  [000]   202.652833: lock_acquired: &sb->s_type->i_mutex_key (16.005 us)

As shown above, the "lock acquired" field is followed by the time
it has been waiting for the lock. Usually, a lock contended entry
is followed by a near lock_acquired entry with a non-zero time waited.

Signed-off-by: Frederic Weisbecker <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Cc: Steven Rostedt <[email protected]>
LKML-Reference: <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Frederic Weisbecker 2009-04-06 01:49:33 +02:00 • committed by Ingo Molnar
commit 2062501ae6
2 changed files with 22 additions and 9 deletions
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8
kernel/lockdep.c
View file

@ -3061,6 +3061,8 @@ found_it:
put_lock_stats(stats);
}
DEFINE_TRACE(lock_acquired);
static void
__lock_acquired(struct lockdep_map *lock, unsigned long ip)
{
@ -3099,6 +3101,8 @@ found_it:
hlock->holdtime_stamp = now;
}
trace_lock_acquired(lock, ip, waittime);
stats = get_lock_stats(hlock_class(hlock));
if (waittime) {
if (hlock->read)
@ -3137,14 +3141,10 @@ void lock_contended(struct lockdep_map *lock, unsigned long ip)
}
EXPORT_SYMBOL_GPL(lock_contended);
DEFINE_TRACE(lock_acquired);
void lock_acquired(struct lockdep_map *lock, unsigned long ip)
{
unsigned long flags;
trace_lock_acquired(lock, ip);
if (unlikely(!lock_stat))
return;