This patch moves a wakened task back to the optimistic spinning loop if the owner is running.
Signed-off-by: Waiman Long <[email protected]> --- kernel/futex.c | 20 ++++++++++++++++---- 1 files changed, 16 insertions(+), 4 deletions(-) diff --git a/kernel/futex.c b/kernel/futex.c index ddc24d1..cca6457 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -3215,8 +3215,8 @@ static inline int futex_spin_trylock(u32 __user *uaddr, u32 *puval, * loop. Preemption should have been disabled before calling this function. * * The number of spinners may temporarily exceed the threshold due to - * racing (the spin count check and add aren't atomic), but that shouldn't - * be a big problem. + * racing and from waiter joining the OSQ(the spin count check and add + * aren't atomic), but that shouldn't be a real problem. */ static inline int futex_optspin(struct futex_q_head *qh, struct futex_q_node *qn, @@ -3297,7 +3297,7 @@ static noinline int futex_spin_lock(u32 __user *uaddr, unsigned int flags) struct futex_q_node qnode; union futex_key key; struct task_struct *owner; - bool gotlock; + bool gotlock, slept; int ret, cnt; u32 uval, vpid, old; @@ -3345,6 +3345,7 @@ static noinline int futex_spin_lock(u32 __user *uaddr, unsigned int flags) owner = ACCESS_ONCE(qh->owner); if ((FUTEX_SPINCNT(qh) < futex_spincnt_max) && (!owner || owner->on_cpu)) +optspin: if (futex_optspin(qh, &qnode, uaddr, vpid)) goto penable_out; @@ -3356,7 +3357,7 @@ static noinline int futex_spin_lock(u32 __user *uaddr, unsigned int flags) list_add_tail(&qnode.wnode, &qh->waitq); __set_current_state(TASK_INTERRUPTIBLE); spin_unlock(&qh->wlock); - gotlock = false; + slept = gotlock = false; for (;;) { ret = get_user(uval, uaddr); if (ret) @@ -3393,7 +3394,16 @@ static noinline int futex_spin_lock(u32 __user *uaddr, unsigned int flags) break; } + /* + * Go back to spinning if the lock owner is running and the + * spinner limit hasn't been reached. + */ + if (slept && (!owner || owner->on_cpu) && + (FUTEX_SPINCNT(qh) < futex_spincnt_max)) + break; + schedule_preempt_disabled(); + slept = true; /* * Got a signal? Return EINTR @@ -3427,6 +3437,8 @@ dequeue: } } spin_unlock(&qh->wlock); + if (!ret && !gotlock) + goto optspin; penable_out: preempt_enable(); -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
