[PATCH 6/6] futex: Add aggressive adaptive spinning argument to FUTEX_LOCK

[Darren Hart <dvhltc@us.ibm.com>]

Aggresive adaptive spinning (aas) allows for more than spinner in the
adaptive loop at a given time. In some scenarios this yields better
results than the default single spinner mode.

Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
---
 kernel/futex.c |   21 ++++++++++++++++++---
 1 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index af61dcd..ddbd158 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2462,6 +2462,9 @@ static int trylock_futex_adaptive(u32 __user *uaddr, ktime_t *timeout)
  * @flags:  futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, FLAGS_ADAPTIVE, etc.)
  * @detect: detect deadlock (1) or not (0)
  * @time:   absolute timeout
+ * @aas:    aggressive adaptive spinning (1) allow multiple spinners (0) allow
+ *          only one spinner. Only valid in conjunction with the FLAGS_ADAPTIVE
+ *          flag.
  *
  * futex_(un)lock() define a futex value policy and implement a full mutex. The
  * futex value stores the owner's TID or'd with FUTEX_WAITERS and/or
@@ -2476,12 +2479,14 @@ static int trylock_futex_adaptive(u32 __user *uaddr, ktime_t *timeout)
  *  0 - On success
  * <0 - On error
  */
-static int futex_lock(u32 __user *uaddr, int flags, int detect, ktime_t *time)
+static int futex_lock(u32 __user *uaddr, int flags, int detect, ktime_t *time,
+                      int aas)
 {
 	struct hrtimer_sleeper timeout, *to = NULL;
-	struct futex_hash_bucket *hb;
 	struct futex_q q = FUTEX_Q_INIT;
+	struct futex_hash_bucket *hb;
 	int ret = 0;
+	u32 uval;
 
 	if (refill_pi_state_cache())
 		return -ENOMEM;
@@ -2497,6 +2502,14 @@ static int futex_lock(u32 __user *uaddr, int flags, int detect, ktime_t *time)
 retry:
 #ifdef CONFIG_SMP
 	if (flags & FLAGS_ADAPTIVE) {
+		if (!aas) {
+			ret = get_user(uval, uaddr);
+			if (ret)
+				goto out;
+			if (uval & FUTEX_WAITERS)
+				goto skip_adaptive;
+		}
+
 		preempt_disable();
 		ret = trylock_futex_adaptive(uaddr, time);
 		preempt_enable();
@@ -2512,6 +2525,8 @@ retry:
 			goto out;
 	}
 #endif
+
+skip_adaptive:
 	q.key = FUTEX_KEY_INIT;
 	ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key);
 	if (unlikely(ret != 0))
@@ -2852,7 +2867,7 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
 		flags |= FLAGS_ADAPTIVE;
 	case FUTEX_LOCK:
 		if (futex_cmpxchg_enabled)
-			ret = futex_lock(uaddr, flags, val, timeout);
+			ret = futex_lock(uaddr, flags, val, timeout, val3);
 		break;
 	default:
 		ret = -ENOSYS;
-- 
1.6.3.3