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


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