centos man page for __wake_up_sync_key

__WAKE_UP_SYNC_KEY(9)						   Driver Basics					     __WAKE_UP_SYNC_KEY(9)

NAME
       __wake_up_sync_key - wake up threads blocked on a waitqueue.

SYNOPSIS
       void __wake_up_sync_key(wait_queue_head_t * q, unsigned int mode, int nr_exclusive, void * key);

ARGUMENTS
       q
	   the waitqueue

       mode
	   which threads

       nr_exclusive
	   how many wake-one or wake-many threads to wake up

       key
	   opaque value to be passed to wakeup targets

DESCRIPTION
       The sync wakeup differs that the waker knows that it will schedule away soon, so while the target thread will be woken up, it will not be
       migrated to another CPU - ie. the two threads are 'synchronized' with each other. This can prevent needless bouncing between CPUs.

       On UP it can prevent extra preemption.

       It may be assumed that this function implies a write memory barrier before changing the task state if and only if any tasks are woken up.

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014						     __WAKE_UP_SYNC_KEY(9)